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Carbon dioxide is a colorless and non-flammable gas at normal temperature and pressure. Although much less abundant than nitrogen and oxygen in Earth's atmosphere, carbon dioxide is an important constituent of our planet's air. A molecule of carbon dioxide (CO ₂) is made up of one carbon atom and two oxygen atoms.

Carbon dioxide is an important greenhouse gas that helps to trap heat in our atmosphere. Without it, our planet would be inhospitably cold. However, a gradual increase in CO ₂ concentrations in Earth's atmosphere is helping to drive global warming, threatening to disrupt our planet's climate as average global temperatures gradually rise.

Carbon dioxide is the fourth most abundant component of dry air. It has a concentration of about 400 ppmv (parts per million by volume) in Earth's atmosphere. Scientists estimate that before human industrial activity, CO ₂ concentration was around 270 ppmv. Carbon dioxide levels in our atmosphere have thus risen about 40% since the onset of human industrialization, and are expected to play a troubling role in raising global temperature. Atmospheric carbon dioxide concentrations have varied substantially in the pre-human history of our planet, and have had profound impacts on global temperatures in the past.

Carbon dioxide plays a key role in Earth's carbon cycle, the set of processes that cycle carbon in many forms throughout our environment. Volcanic outgassing and wildfires are two significant natural sources of CO ₂ in Earth's atmosphere. Respiration, the process by which organisms liberate energy from food, emits carbon dioxide. When you exhale, it is carbon dioxide (amongst other gases) that you breathe out. Combustion, whether in the guise of wildfires, as a result of slash-and-burn agricultural practices, or in internal combustion engines, produces carbon dioxide.

Photosynthesis, the biochemical process by which plants and some microbes create food, uses up carbon dioxide. Photosynthetic organisms combine CO ₂ and water (H ₂O) to produce carbohydrates (such as sugars) and emit oxygen as a by-product. Places such as forests and areas of the ocean that support photosynthetic microbes, therefore, act as massive carbon "sinks", removing carbon dioxide from the atmosphere via photosynthesis. Earth's early atmosphere had much higher CO ₂ levels and almost no oxygen; the rise of photosynthetic organisms led to an increase in oxygen which enabled the development of oxygen-breathing creatures such as us!

Burning generates CO ₂, although incomplete combustion due to limited oxygen supply or an excess of carbon can also produce carbon monoxide (CO). Carbon monoxide, a dangerous pollutant, eventually oxidizes to carbon dioxide.

Small canisters containing pressurized CO ₂ are used to inflate bicycle tires and life jackets and to power paintball guns. The "fizz" in soda pop is supplied by carbon dioxide. Carbon dioxide is also released by yeast during fermentation, giving beer its head and making champagne bubbly. Because it is not flammable, CO ₂ is used in some fire extinguishers. Carbon dioxide forms a weak acid, called carbonic acid (H ₂CO ₃), when dissolved in water.

Carbon dioxide is the most abundant gas in the atmospheres of Mars and Venus. Solid, frozen carbon dioxide is called "dry ice". The polar ice caps of Mars are a mixture of normal water ice and dry ice. Liquid CO ₂ only forms at pressures higher than about 5 times the atmospheric pressure on Earth at sea level, so in many situations dry ice does not melt into a liquid form. Instead, it goes directly from a solid state to a gaseous state in a process called sublimation.

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Carbon dioxide is a colorless and non-flammable gas at normal temperature and pressure. Although much less abundant than nitrogen and oxygen in Earth's atmosphere, carbon dioxide is an important constituent of our planet's air.

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The earth's Atmospheric CO2 level is increasing day by day. The global average atmospheric carbon dioxide in 2019 was 409.8 parts per million and in October-2020 it is 411.29. Carbon dioxide is a key greenhouse gas and responsible for about three-quarters of emissions. So CO2 level monitoring has also started to gain importance.

In our previous project, we used the Gravity Infrared CO2 sensor to measure the CO2 concentration in air. In this project, we are going to use an MQ-135 sensor with Arduino to measure the CO2 concentration. The measured CO2 concentration values will be displayed on the OLED module and last we will also compare the Arduino MQ-135 sensor readings with Infrared CO2 sensor readings. Apart from CO2, we have also measured the concentration of LPG, Smoke, and Ammonia gas using Arduino.

Components Required

Arduino Nano

MQ-135 Sensor

Jumper Wires

0.96' SPI OLED Display Module

Breadboard

22KΩ Resistor

0.96' OLED Display Module

OLED (Organic Light-Emitting Diodes) is a self light-emitting technology, constructed by placing a series of organic thin films between two conductors. A bright light is produced when an electric current is applied to these films. OLEDs are using the same technology as televisions, but have fewer pixels than in most of our TVs.

For this project, we are using a Monochrome 7-pin SSD1306 0.96" OLED display. It can work on three different communications Protocols: SPI 3 Wire mode, SPI four-wire mode, and I2C mode. You can also learn more about the basics of OLED display and its types by reading the linked article. The pins and its functions are explained in the table below:
OLED Specifications:

OLED Driver IC: SSD1306

Resolution: 128 x 64

Visual Angle: >160°

Input Voltage: 3.3V ~ 6V

Pixel Colour: Blue

Working temperature: -30°C ~ 70°C

Preparing the MQ-135 Sensor

MQ-135 Gas Sensor is an air quality sensor for detecting a wide range of gases, including NH3, NOx, alcohol, benzene, smoke, and CO2. MQ-135 sensor can either purchased as a module or just as a sensor alone. In this project, we are using an MQ-135 sensor module to measure CO2 concentration in PPM. The circuit diagram for the MQ-135 board is given below:

The load resistor RL plays a very important role in making the sensor work. This resistor changes its resistance value according to the concentration of gas. According to the MQ-135 datasheet, the load resistor value can range anywhere from 10KΩ to 47KΩ. The datasheet recommends that you calibrate the detector for 100ppm NH3 or 50ppm Alcohol concentration in air and use a value of load resistance (RL) of about 20 KΩ. But if you track your PCB traces to find the value of your RL in the board, you can see a 1KΩ (102) load resistor.

So to measure the appropriate CO2 concentration values, you have to replace the 1KΩ resistor with a 22KΩ resistor.

Circuit Diagram to Interface MQ135 with Arduino

The complete schematics to connect MQ-135 Gas Sensor with Arduino is given below:

The circuit is very simple as we are only connecting the MQ-135 Sensor and OLED Display module with Arduino Nano. MQ-135 Gas Sensor and OLED Display module both are powered with +5V and GND. The Analog Out pin of the MQ-135 sensor is connected to the A0 pin of Arduino Nano. Since the OLED Display module uses SPI communication, we have established an SPI communication between the OLED module and Arduino Nano. The connections are shown in the below table:

After connecting the hardware according to the circuit diagram, the Arduino MQ135 sensor setup should look something like below:

Calculating the Ro Value of MQ135 Sensor

Now that we know the value of RL, let's proceed on how to calculate the R o values in clean air. Here we are going to use MQ135.h to measure the CO2 concentration in the air. So first download the MQ-135 Library, then preheat the sensor for 24 hours before reading the R o values. After the preheating process, use the below code to read the R o values:

#include "MQ135.h"
void setup (){
Serial.begin (9600);
}
void loop() {
MQ135 gasSensor = MQ135(A0); // Attach sensor to pin A0
float rzero = gasSensor.getRZero();
Serial.println (rzero);
delay(1000);
}

Now once you got the R o values, Go to Documents > Arduino > libraries > MQ135-master folder and open the MQ135.h file and change the RLOAD & RZERO values.

///The load resistance on the board
#define RLOAD 22.0
///Calibration resistence at atmospheric CO2 level
#define RZERO 5804.99

Now scroll down and replace the ATMOCO2 value with the current Atmospheric CO2 that is 411.29

///Atmospheric CO2 level for calibration purposes
#define ATMOCO2 397.13

Code to Measure CO2 Using Arduino MQ135 Sensor

The complete code for interfacing MQ-135 Sensor with Arduino is given at the end of the document. Here we are explaining some important parts of the MQ135 Arduino code.

The code uses the Adafruit_GFX, and Adafruit_SSD1306, and MQ135.h libraries. These libraries can be downloaded from the Library Manager in the Arduino IDE and install it from there. For that, open the Arduino IDE and go to Sketch < Include Library < Manage Libraries. Now search for Adafruit GFX and install the Adafruit GFX library by Adafruit.

Similarly, install the Adafruit SSD1306 libraries by Adafruit. MQ135 library can be downloaded from here.

After installing the libraries to Arduino IDE, start the code by including the needed libraries files.

#include "MQ135.h"
#include <SPI.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Then, define the OLED width and height. In this project, we're using a 128×64 SPI OLED display. You can change the SCREEN_WIDTH, and SCREEN_HEIGHT variables according to your display.

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Then define the SPI communication pins where OLED Display is connected.

#define OLED_MOSI   9
#define OLED_CLK   10
#define OLED_DC    11
#define OLED_CS    12
#define OLED_RESET 13

Then, create an Adafruit display instance with the width and height defined earlier with the SPI communication protocol.

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, OLED_MOSI, OLED_CLK, OLED_DC, OLED_RESET, OLED_CS);

After that, define the Arduino pin where the MQ-135 sensor is connected.

int sensorIn = A0;

Now inside the function, initialize the Serial Monitor at a baud rate of 9600 for debugging purposes. Also, Initialize the OLED display with the function.

Serial.begin(9600);
display.begin(SSD1306_SWITCHCAPVCC);
display.clearDisplay();

Inside the function, first read the signal values at the Analog pin of Arduino by calling the analogRead() function.

val = analogRead(A0);
  Serial.print ("raw = ");

Then in the next line, call the gasSensor.getPPM() to calculate the PPM values. The PPM values are calculated using the Load resistor, R 0, and reading from the analog pin.

 float ppm = gasSensor.getPPM();
  Serial.print ("ppm: ");
  Serial.println (ppm);

After that, set the text size and text colour using the setTextSize() and setTextColor().

display.setTextSize(1);
display.setTextColor(WHITE);

Then in the next line, define the position where the text starts using the setCursor(x,y) method. And print the CO2 Values on OLED Display using the display.println() function.

   display.setCursor(18,43);
  display.println("CO2");
  display.setCursor(63,43);
  display.println("(PPM)");
  display.setTextSize(2);
  display.setCursor(28,5);
  display.println(ppm);

And in the last, call the display() method to display the text on OLED Display.

 display.display();
 display.clearDisplay();

Testing the Interfacing of MQ-135 Sensor with Arduino

Once the hardware and code are ready, it is time to test the sensor. For that, connect the Arduino to the laptop, select the Board and Port, and hit the upload button. Then open your serial monitor and wait for some time (preheat process), then you'll see the final data. The Values will be displayed on OLED display as shown below:

This is how an MQ-135 sensor can be used to measure accurate CO2 in the air. The complete MQ135 Air Quality Sensor Arduino Code and working video are given below. If you have any doubts, leave them in the comment section.

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Measuring CO2 Concentration in Air using Arduino and MQ-135 Sensor

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In this project, we are going to use MQ-135 sensor with Arduino to measure the CO2 concentration in PPM and display it on OLED.

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In order to measure CO2 gas accurately, you must know how much CO2 you want to measure.

With all the various carbon dioxide meters, monitors and sensors we offer, it may feel overwhelming to choose between them. That's why one of the first questions we ask is, "What are you trying to measure?" This question helps us determine the range of CO2 levels, which narrows down the list of products we offer that can work for a particular application.

Since we offer devices and sensors that measure up to 100% CO2, it seems like the simple answer would be " give me a sensor that will measure everything!" The problem with this answer is that the wider the range of CO2 levels to be measured, the lower the accuracy. Conversely, the narrower the range, the more accurate each measurement will be.

It may help to start out by describing how CO2 is measured. For most products, the CO2 level is measured as a percentage of a volume of air, either as % by volume or as parts-per-million (ppm).

What does ppm - parts per million stand for?

Parts-per-million(abbreviated ppm) is the ratio of one gas or other molecule to another. For example, 1,000 ppm of CO2 means that there are 1,000 molecules of CO2 and 999,000 molecules of other gases or water vapor.

In other words, 1 ppm = 0.0001% gas.

Learn more about parts per million here.

Measuring CO2 in parts per million

While percentages are easy to understand, ppm can seem a bit more confusing. Here is a thought-experiment that may help.

Imagine you were given a box with 1 million molecules of typical outdoor air. You need to count the molecules by hand.

Remember, this is a thought-experiment!

By the time you got to the bottom of the box, you'll have counted about 780,000 (or 78%) nitrogen molecules, 209,000 (or 20.9%) oxygen molecules, and 9,000 (or 0.9%) molecules of argon gas. Water vapor (H20) could also account for some of the molecules, but let's ignore it for this example.

Once you've added up 998,000 (99.8%) of the nitrogen, oxygen and argon molecules, you'll still have about 2,000 remaining molecules in several small piles. These will be other gases like CO2, neon, methane and helium.

The biggest of these small piles would be the CO2 molecules. There will be about 400 of them, or 0.04% of the total. But instead of saying "four one-hundredths of a percent," you would say, you counted 400 CO2 molecules, or 400 parts-per-million. Scientists abbreviate this as ppm.

In general, percentages of gas in air samples below 1% are measured in parts-per-million. Here's a table that shows how to convert percentages to ppm:

What percentage of CO2 do you need to measure?

Different CO2 sensors can measure anywhere between 0 ppm and 100% CO2 in a gas by volume. In order to know what percentage of carbon dioxide you need to measure, you need to understand the application or industry you are in. From there, our team can best determine the range, accuracy, or precision you will need to recommend the proper carbon dioxide sensor that is best suited for your application. For example:

How is CO2 measured?

In order to measure carbon dioxide in air, a CO2 sensor is used. The most common type is the NDIR non-dispersive infrared sensor. It is popular due to its long life-span, speed, and low cross-sensitivity to other gases.

An NDIR CO2 sensor works by measuring infrared light in an air sample. The amount of infrared light absorbed by the molecules of carbon dioxide is proportional to the number of CO2 molecules in the air sample. This allows the sensor to measure the amount of CO2.

For example the S8 Miniature 5% CO2 Sensor can measure from 400 ppm to 5% CO2, yet it has less than a 30x20x10mm footprint and runs on only 30mA.

Note that there are other ways to measure dissolved CO2: in blood, in a liquid like water or in beer.

CO2 Measurement Range vs. Accuracy

So what does carbon dioxide sensing have to do with accuracy? As a rule, the narrower the range of CO2 measured, the higher the accuracy of the sensor.

For example, if you were measuring 400 ppm CO2 (fresh air) using a 100% CO2 sensor and the CO2 level increased to 500 ppm, the change would be from 0.04% to 0.05%. This 0.01% (100 ppm) change is outside the 100-300 ppm range of accuracy of a typical 100% CO2 sensor. The sensor would probably not record any change.

However, the accuracy of a 10,000 ppm NDIR sensor is around 50 ppm (0.005%). This means that while you might not see an exact 100 ppm change, you'd see a rise between 50 ppm and 150 ppm CO2. Depending on the precision of the sensor, the rise would trend toward 100 ppm, which is what you originally wanted to measure.

By knowing the range of the CO2 levels you need to measure, we can narrow down the list of products we offer that will be the most accurate for your application.

CO2 Measurement Accuracy vs. Precision

Did you notice that the word precision was mentioned above? Accuracy and precision mean two different things when it comes to carbon dioxide sensors.

In the simplest terms, given a set of data points from repeated measurements of the same quantity, the set can be said to be precise if the values are close to each other, while the set can be said to be accurate if their average is close to the true value of the quantity being measured. The two concepts are independent of each other, so a particular set of data can be said to be either accurate, or precise, or both, or neither.

For NDIR CO2 sensors, accuracy is the difference between the amount of CO2 measured and the theoretical exact amount of CO2 in a gas sample. Precision isn't measured. Instead, NDIR CO2 sensors rely on increasing the sample size and average CO2 reported readings to increase the precision.

For example, sensor manufacturers list accuracy as ± ppm ± a percentage of the reading. Take the K30 10,000ppm sensor, which lists it's accuracy as ± 30 ppm ± 3%. This means that a K30 calibrated at 400 ppm could report a single measurement anywhere between

NDIR CO2 sensors take a new reading anywhere from 20 times a second to once every 30 seconds. As each reading is taken the sensor's on-board software takes into account all the previous measurements and report the average. This solves the problem of precision. If you want a more precise CO2 reading, look for a sensor with a higher frequency of measurements.

CO2 Measurement and Safety

Because carbon dioxide is an odorless, colorless, and tasteless gas, too much exposure can result in negative health effects or fatality. Whenever carbon dioxide gas is used, stored, or produced in high volumes, high concentrations can quickly occur. Because high levels of CO2 are hard to monitor, carbon dioxide sensors are used to warn occupants if a leak occurs. CO2 sensors can quickly and accurately monitor indoor ambient levels to protect employees, staff, and establishments from injury or hazard.

It is not that difficult to monitor carbon dioxide gas when you have the proper technology, monitor, or sensor. While carbon dioxide monitoring is required in many different scenarios and industries, we ensure our customers select the best solution to fit their application.

For more information on carbon dioxide sensors, contact us.

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How to Measure Carbon Dioxide (CO2) Accurately

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CO2 measurement in air: everything you need to know. Range, accuracy and precision. Percentage versus parts per million.

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Most of us know the effects of bad air in meeting rooms and classrooms. You get tired and less alert. Bad air is directly connected to the level of CO2 in a room, due to insufficient ventilation. Just quickly opening a window will remedy the effects of bad air.

Not only do higher levels CO2 make you drowsier, but it also increases the risk of headaches, gives people with allergies a harder time and even decreases our capabilities for strategic and innovative thinking.

After reading this tutorial you will be able to build your own CO2 sensor unit and regulate the level of fresh air at your apartment, office, classroom or wherever.

What you will learn in this project:

The following instructions are provided to assist you in developing this CO2 sensor unit that can:

Measure the CO2 levels in the air.

Record CO2 at regular intervals (store a value and timestamp).

Display the current CO2 level being measured, as well as: temperature, air pressure and humidity through our IoT platform "Wappsto" through a wapp.

Optional: It is recommended that before attempting this build you have completed the Blinking and LED tutorial found here: https://wappsto.seluxit.com/led-hello-world/

While working on this circuit, try to enjoy the process and know that troubleshooting is an important part of building circuits and research in general! Even individuals very experienced with micro-controllers and circuits will spend a lot of time debugging.

What you will need for this project:

1x SCD30 CO2 Sensor Module

1x SparkFun Atmospheric Sensor Breakout - BME280

5x Female-to-Male and Male-to-Male Dupont wires

The whole process will be split into 5 steps:

Initial preparations: where we will explain how to set up your device in Wappsto and do a bit of code editing on the Pi

Assembling: where we show you how to correctly wire up the two sensors to the Pi

Connecting: where we will show you how to test the wiring of the device

Installation and reporting: where we will show you what to install and run on the device in order to start receiving reports

Wapp UI creation: we also provide you with some example and code to create a UI for your device in Wappsto

Step 1 : Initial preparations

We will start off by creating our device in Wappsto and download the python code which we will edit and upload to our Pi as we did it our previous tutorial about creating Blinking LED.

Here is the IoT model made in this tutorial.

You can create the whole thing manually by creating a Network, Device and Values and filling out all the required fields.

Or you can create it by copy-pasting this JSON file: https://raw.githubusercontent.com/Wappsto/IoT_RapidPrototyping/master/co2/CO2dataModelSpecification.json

Note: ifyou decide to create the Network, Device and Values and you use different namesmake sure to change them in the code later on, if you are not sure how to continue with this step please refer to our previous tutorial https://wappsto.seluxit.com/led-hello-world/

When we have set up our Network, Device and Values we can download the python code which we will modify a bit and then upload to our Pi.

After you have downloaded the python code open the folder and with an editor of your choice open the peripherals.py and change:

with the following code:

from values import environment
class Peripherals:
 def __init__(self, sendQueue):
 self.env = environment.Environment(sendQueue)
 def get_value_sensors_co2(self):
 return self.env.get_co2()
 def get_value_sensors_temperature(self):
 return self.env.get_temperature()
 def get_value_sensors_pressure(self):
 return self.env.get_pressure()
 def get_value_sensors_humidity(self):
 return self.env.get_humidity()

Then you need to download the following "values" folder containing the following code files:

which you can download from our GitHub page

These files represent our two sensors as well as the settings for what the Pi will take from them and when reports with that data will be sent. We will upload this folder to our Pi later in Step 4.

In the "environment" file you can change the interval frequency for receiving the reports from the device.

Note that we have set it up to 5 seconds but inorder to use less data we advise that you increase that number.

You can easily do that by changing self.measurement_interval=5 to the time which you would like to receive the reports (the time is measured in seconds). For more information about the data traffic please refer to the Data plans in the left menu Payment Plan.

Step 2 : Assembling

After setting up the device in Wappsto and editing the code we can start wiring our device together.

We have soldered our parts in advance so if you are unsure about how to do that please refer to https://www.makerspaces.com/how-to-solder/ or any other reference you feel comfortable with.

We can start with setting up the SCD30 CO2 Sensor Module, note that we are only using the four pins shown in the following figure 2 (VDD, GND, TX/SCL and RX/SDA):

Next, we can set up the BME280, here we will be using again only the four pins on the left side (GND, 3.3V, SDA and SCL) referring to figure 3.

Once we have set up our two sensors on the breadboard, we can start wiring all them along with the Raspberry Pi, refer to figures 3 and 4.

Please follow carefully the wiring in order to avoid errors.

Here is how our CO2 sensor looks. So far so good. We have wired up all our parts and now it's time to see if we did it correctly, which will we will check in the next Step.

Step 3 : Connecting

After we have wired up our SCD30, BME280 and the Raspberry Pi3 its time to connect to it and test the wiring.

This tutorial is written for Windows users, however, if you are a Linux or Mac user you can just use a terminal to do "ssh" and "scp" instead of using WinSCP and PuTTY as we have used in this example, which we have shown in our previous tutorial referred here: https://www.seluxit.com/led-hello-world/

Startup PuTTY and connect to your Pi, here we run:

sudo apt-get install rpi.gpiowiringpi python3-dev python3-pip i2c-tools
sudo apt-get update

After that we need to enable the "i2cdetect" option, run:
InterfacingOptions > I2C > Yes
After we enable the I2C detect its finally time to test the wiring, run:

If your wiring was done correctly you should get the following result

Here "61" corresponds to the SCD30 and the "77" to the BME280 sensors. If your results or you don't see these numbers double check your wiring and make sure all parts and wires are connected and plugged in correctly (pay careful attention to the wiring as any missing line will stop the device from working/being displayed).

Step 4 : Installing and running

So, after setting up the code, wiring up the device and checking the connection, its time to upload the code to the Pi, install and run our program.

Since this tutorial is made for Windows, start WinSCP and log into your Pi, then upload the "values" folder and upload it to the Pi as shown in the example.

Note that you can change the code just remember to upload the file onto the Pi once you have done so.

Once that is done open up PuTTY and run:

sudo pip3 installsmbus2 numpy

After that go in the corresponding folder in your Pi like shown in the following example:

cd 12d53bd7-4954-40a0-a5cf-ee9c39c4681a

and then run:

if everything is done correctly you should start receiving reports from your sensors

You can go back to Wappsto > My Data > Co2 (or how you chose to name your Network) and there you can also see the reports and refresh them at any time.

Remember to shut down your Raspberry Pi before unplugging the power cable.

Step 5 : Wapp UI creation

We have covered this step in our previous tutorial as well at https://wappsto.seluxit.com/led-hello-world/

Once we have our device connected and set up, we can make a simple or complex (depending on your personal preferences) wapp UI for our connected device see figure 5 as an example.

You can find some example files for one of our sensors on our GitHub page

You can now measure the levels of CO2 in ppm, as well as temperature in Celsius, air pressure in Pa and humidity in %. You can make different versions of this sensor and add additional sensors, lights, or even a display, your imagination is the limit.

You can see some of our other CO2 devices here: https://www.seluxit.com/firefly/https://github.com/Wappsto/wapps/tree/master/smart-home-sensors/foreground

And finally, the next question which needs to be answered is: How will we solve this problem when the CO2 level of the atmosphere is much higher ?

You can read a few very interesting articles and discussions on that topic by http://co2brains.org/https://medium.com/swlh/does-co2-harm-your-body-d20b4a0d03c1
Combating CO2:
https://www.youtube.com/playlist?list=PLBygmqSJrqK5dgCpmIugTUSskb7dNr07n
Thank you for the read and participation!

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A quick and easy guide for making your own carbon-dioxide sensor unit to measure the percentage of carbon dioxide gas. Find this and other hardware projects on Hackster.io.

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How to Measure Co2 - Setup and Code a MQ135 CO2 Sensor

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LibreCO2: Simple CO2 meter using Arduino UNO and CO2 low cost sensor (Sensirion SCD30, Winsen MH-Z14 or MHZ-19 and Cubic CM1106).

This is a simple and low cost sensor version of a CO2 meter built with the most common materials on the market: an Arduino UNO and the three most popular low cost REAL CO2 sensors: Sensirion SCD30, Winsen MH-Z14 or 19 and Cubic CM1106. LibreCO2 uses an Arduino UNO but can be extended to MEGA or nano, that are very popular in schools and frequently used in technology and the electronics classes. Also, the majority of schools have many of them.

The code is the most basic and the.hex file is published for the programming of the Arduino with the software Xloader. You don't have to install Arduino software to compile and program the code. If you are searching for Wi-Fi or Bluetooth connectivity, you can find many open source alternatives on a list at the end of the guide, for example CanAirIO. The CO2 meter uses the most popular components on the market, not the most advanced, and the simplest building without the need of an iron solder.

All the sensors used are NDIR, which is the actual standard for real CO2 measurements:
https://www.co2meter.com/blogs/news/6010192-how-does-an-ndir-co2-sensor-work
The code and more information are available in the github repository:
https://github.com/danielbernalb/LibreCO2 Materials:
There are two options for the sensor assembly: the easiest is using an Arduino Multifunction Shield (Shield), which already includes a 4-digit display, buzzer and buttons, making the assembly much easier. The second is assembling the parts individually.

1. Multi-function Shield option:

Arduino Multifunction Shield.

Arduino UNO, the original or Chinese version. The difference is the driver installation. Both are very easy to find in any country and work well. The original (right) and clone (left):

(4) Jumper cables, female - female.
Sensor, options:
a. Sensirion SCD30, is the most expensive (US$52) but delivers the best performance. Sensirion has distributors in USA and Europe. Example: https://www.mouser.com/ProductDetail/Sensirion/SCD30/?qs=rrS6PyfT74fdywu4FxpYjQ%3D%3D

Pros: excellent performance (fast & reliable), expedited shipping from USA or Europe.

The Modbus protocol is used for the connection between the Arduino and the sensor which allows the direct connection between the Arduino and the sensor without the use of a hardware data driver. You must connect the SEL pin with the VIN pin of the sensor using a 100 kΩ (kilo ohms) resistance as seen in the pictures and video to activate the Modbus protocol.

b. Winsen MH-Z14 or 19, one of the cheapest and most popular, good performance, some maybe slow. Beware of fake clones!!!

Pros: acceptable performance (slow compared with Sensirion, medium reliable), low price (18 dollars including shipping from Aliexpress)

Cons: slow shipping with Aliexpress, standard shipping (6-20 weeks), fake copies (you have to be careful, its recommended only buying from an official store).

Only buy MH-Z19 from the Winsen Supplier in Aliexpress, the market is flooded with fake copies, more info in: https://youtu.be/5_QQe75-SZI or in spanish https://emariete.com/sensores-co2-mh-z19b-falsos/

Original at Aliexpress: https://es.aliexpress.com/item/1005001865093513.html

c. Cubic CM1106, is the last option because the distribution in China is for second-hand units and sometimes not available. https://www.aliexpress.com/item/4001082699057.html
Connections for each sensor: Sensirion SCD30
Shield PIN ---> Sensor

GND ---> GND

+5 ---> VIN

5 ---> RX/SDA

6 ---> TX/SCL
Winsen MH-Z19B sensor
GND ---> GND

+5 ---> VIN

5 ---> RX

6 ---> TX
Winsen MH-Z14A sensor
GND ---> 5 or 16 pin connector

+5 ---> 4 or 17 pin connector

5 ---> 3 o 18 pin connector

6 ---> 2 o 19 pin connector
Cubic CM1106 sensor
GND ---> G Pin 2 a 4-pin connector

+5 ---> V1 Pin 1 a 4-pin connector

5 ---> R Pin 2 a 5-pin connector

6 ---> T Pin 3 a 5-pin connector

Assembly video

(in Spanish with English subtitles):

3. Program / Burn the Firmware (the code in the Arduino).

There are three options for the program of the Arduino: the easiest is using an Android cell phone and an USB OTG cable, the second is using a PC with the software Xloader and the last is installing Arduino on your PC.
1. Android cell phone.

Connect the USB OTG cable to the cell phone.

Install the Android app "Arduino Hex Uploader-Firmware Bin Upload".

Dowload the .hex file from this Google Drive directory based on your sensor version (Shield and brand sensor).

Browse the .hex file in your cell phone.

Upload the code to your Arduino board.

FINISH.

Programming / burning video (in Spanish with English subtitles):
2. Using your PC with Xloader software (only Windows):
1. Connect the Arduino to your computer. If the driver is not automatically detected, you will have to identify if your Arduino is the original or a Chinese clone:

1.1. If the Arduino is a Chinese version, please follow the instructions on this web page: https://www.arduino.cc/en/Guide/ArduinoUno

1.2. If the Arduino is chinese version please follow the instructions in this web page: https://learn.sparkfun.com/tutorials/how-to-install-ch340-drivers

2. After installing the driver, you have 2 options:

2.1. The easy option is to use the Xloader software in the folder, of the repository, with the same name:

The left screenshot shows the window that Xloader displays when it starts.
https://drive.google.com/drive/folders/1FxXLVhaGF6UCVObQlh8cVLddyWyQqUT0
Explore until you find the.hex file that you are going to load into the Arduino. Each sensor version (Sensirion, Winsen or Cubic) is available in the "hex files" directory. Example: "LibreCO2_Shield_SCD30.hex" is the file for the Sensirion SCD30 sensor with the Multi-function Shield version. Note: Don't download it directly from the page with the "Save As" option, that ruins the file. Use the following link of Google Drive to download your Sensor version (SCD30, MHZ14_9 or CM1106) and build option (with Shield or by Parts):

2.1.2. Select the device type you are going to load into (Uno/ATmega328).

2.1.3. Select the COM port where your Arduino is attached, if you don't know, look for it in the Device Manager "COM and LPT ports".

2.1.4. The baud rate should be 115200.

2.1.5. Press the "Upload" button.
3. If you want to edit and compile the code please install the Arduino software in Windows, Mac or Linux: https://www.arduino.cc/en/software
2.1.6. When the.hex file has been loaded into the Arduino, the right screenshot, the message of "xxxxx bytes uploaded" appears, if it fails you will get the message of "upload fail"
https://learn.sparkfun.com/tutorials/installing-arduino-ide/all
The following guide explains how to install Arduino on Windows, Mac or Linux and is very explanatory:

YouTube contains hundreds of tutorials on how to install Arduino on different operating systems and on learning the programming. You can also collaborate by improving this code or create your own version.

4. Sensor Operation.

When the Arduino programming has been completed, we have several sensor operating modes and options:

Normal mode: When the sensor is turned on, the BEEP message appears and a number between 700 and 1300 shows the alarm level that we have programmed. Section 3 below explains how to modify it. After that, the meter verifies the connection to the low cost sensor. If a "good" message appears, then connection is well made and the sensor heating process ("heat") will continue, which lasts 30 seconds for the Sensirion and Cubic sensors, and 3 minutes for the Winsen sensors. If the message is "fail" then the connection failed and we must verify the connection between the Arduino and the sensor. After heating up, the CO2 value in parts per million ppm appears on the screen. When the value is higher than the Beep level, the alarm sounds and the shield LEDs flash.

Calibration Mode: Explained in the attached video. Sensor calibration is recommended after sensor assembly and when widely differing measurements are observed outdoors in the 400 ppm range. All these low-cost sensors are calibrated outdoors, placing them in an outdoor space for a few minutes without receiving any direct strong wind because it affects the measurement. Therefore, it is recommended to place them inside a box that avoids direct wind. After fulfilling these conditions, you must press the S1-A1 button in the shield version, or the "switch" in the version by parts, for more than 5 seconds, and the "cal-" message will appear on the screen, counting down 5 minutes for the Sensirion and Cubic and 20 minutes for the Winsen. At the end of this time, the sensor receives the calibration order and is ready to be used again. If you want to interrupt the calibration process, press the S3-A3 button.

BEEP alarm threshold level change mode: Explained in the attached video. To change the alarm level from 1000 ppm, by default, to another value between 700 and 1300 ppm you must press button S2-A2 in the shield version, or place an additional cable or switch from pin A3 to A5 in the parts version, for more than 5 seconds and the message "BEEP" will appear, then the value to which it is programmed. Then you must press the button again to modify the value. When you find it, press the S3-A3 button to program this new BEEP level value.

Normal mode: When the sensor is turned on, the BEEP message appears and a number between 700 and 1300 shows the alarm level that we have programmed. Section 3 below explains how to modify it. After that, the meter verifies the connection to the low cost sensor. If a "good" message appears, then connection is well made and the sensor heating process ("heat") will continue, which lasts 30 seconds for the Sensirion and Cubic sensors, and 3 minutes for the Winsen sensors. If the message is "fail" then the connection failed and we must verify the connection between the Arduino and the sensor. After heating up, the CO2 value in parts per million ppm appears on the screen. When the value is higher than the Beep level, the alarm sounds and the shield LEDs flash.

Should you have any doubts, bugs, or comments please do not hesitate to contact me at danielbernalb@gmail.com or at my twitter account @danielbernalb

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LibreCO2: Easily Build a low cost CO2 monitor with Arduino

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LibreCO2: Simple CO2 meter using Arduino UNO and CO2 low cost popular sensor (Sensirion SCD30, Winsen MH-Z14 or MHZ-19 and Cubic CM1106). Find this and other hardware projects on Hackster.io.

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MH-Z14A CO2 Meter Tutorial with Arduino, ESP8266 or ESP32

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Learn how to use the MH-Z14A CO2 Meter with your Arduino, ESP8266 or ESP32 microcontroller to build you own CO2 alarm for your office and home.

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How does indoor VS outdoor airflow and human movement affect Co2 levels. And what does this mean for the air we breathe and our health indoors.

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CO2 & TVOC Measurement using CCS811 Air Quality Gas Sensor & Arduino

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How to Build a DIY CO2 Meter with Arduino | Atlas Scientific

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In this tutorial, we will show you how to make a benchtop-style CO2 meter using our EZO-CO2™ Embedded Carbon Dioxide Sensor connected to an Arduino Uno. The real-time readings will be shown on a…

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Using the SCD30 with Arduino is a simple matter of wiring up the sensor to your Arduino-compatible microcontroller, installing the Adafruit SCD30 library we've written, and running the provided example code.

I2C Wiring

Here is how to wire up the sensor using one of the STEMMA QT connectors. The examples show a Metro but wiring will work the same for an Arduino or other compatible board.

Connect board VIN (red wire) to Arduino 5V if you are running a 5V board Arduino (Uno, etc.). If your board is 3V, connect to that instead.

Here is how to wire the sensor to a board using a solderless breadboard:

Connect board VIN (red wire) to Arduino 5V if you are running a 5V board Arduino (Uno, etc.). If your board is 3V, connect to that instead.

Library Installation

You can install the Adafruit SCD30 library for Arduino using the Library Manager in the Arduino IDE.

Click the Manage Libraries ... menu item, search for Adafruit SCD30 , and select the Adafruit SCD30 library:

Finally, search for Adafruit Unified Sensor and install that too (you may have to scroll a bit)

Load Example

Open up File -> Examples -> Adafruit SCD30 -> adafruit_scd30_test

After opening the demo file, upload to your Arduino wired up to the sensor. Once you upload the code, you will see the temperature, humidity and eCO2 data values being printed when you open the Serial Monitor ( Tools->Serial Monitor) at 115200 baud, similar to this:

Its normal for the first CO2 reading to be 0, simply ignore the first reading when logging data.

The sensor has a lot going on, there's temperature and humidity reading thanks to an SHT31 sensor on board. These values are used internally to normalize the NDIR CO2 readings as well. You can only get data every 2 seconds, which is pretty fast for this kind of sensor! If you want to slow down the readings to reduce power usage, uncomment this section:

// if (!scd30.setMeasurementInterval(10)){
//   Serial.println("Failed to set measurement interval");
//   while(1){ delay(10);}
// }

The valid range is 2 seconds per reading up to 1800 seconds per reading.

// Basic demo for readings from Adafruit SCD30
#include <Adafruit_SCD30.h>

Adafruit_SCD30  scd30;


void setup(void) {
  Serial.begin(115200);
  while (!Serial) delay(10);     // will pause Zero, Leonardo, etc until serial console opens

  Serial.println("Adafruit SCD30 test!");

  // Try to initialize!
  if (!scd30.begin()) {
    Serial.println("Failed to find SCD30 chip");
    while (1) { delay(10); }
  }
  Serial.println("SCD30 Found!");


  // if (!scd30.setMeasurementInterval(10)){
  //   Serial.println("Failed to set measurement interval");
  //   while(1){ delay(10);}
  // }
  Serial.print("Measurement Interval: ");
  Serial.print(scd30.getMeasurementInterval());
  Serial.println(" seconds");
}

void loop() {
  if (scd30.dataReady()){
    Serial.println("Data available!");

    if (!scd30.read()){ Serial.println("Error reading sensor data"); return; }

    Serial.print("Temperature: ");
    Serial.print(scd30.temperature);
    Serial.println(" degrees C");

    Serial.print("Relative Humidity: ");
    Serial.print(scd30.relative_humidity);
    Serial.println(" %");

    Serial.print("CO2: ");
    Serial.print(scd30.CO2, 3);
    Serial.println(" ppm");
    Serial.println("");
  } else {
    //Serial.println("No data");
  }

  delay(100);
}

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Adafruit SCD-30 - NDIR CO2 Temperature and Humidity Sensor

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The SCD-30 is an NDIR sensor, which is a 'true' CO2 sensor, that will tell you the CO2 PPM (parts-per-million) composition of ambient air. Unlike the SGP30, this sensor isn't approximating it from VOC gas concentration - it really is measuring the CO2 concentration!

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Reader question: I heard that carbon dioxide makes up 0.04 percent of the world's atmosphere. Not 0.4 percent or 4 percent, but 0.04 percent! How can it be so important in global warming if it's such a small percentage?
I am often asked how carbon dioxide can have an important effect on global climate when its concentration is so small - just 0.041 percent of Earth's atmosphere. And human activities are responsible for just 32 percent of that amount.

I study the importance of atmospheric gases for air pollution and climate change. The key to carbon dioxide's strong influence on climate is its ability to absorb heat emitted from our planet's surface, keeping it from escaping out to space.

Early greenhouse science

The scientists who first identified carbon dioxide's importance for climate in the 1850s were also surprised by its influence. Working separately, John Tyndall in England and Eunice Foote in the United States found that carbon dioxide, water vapor and methane all absorbed heat, while more abundant gases did not.

Scientists had already calculated that the Earth was about 59 degrees Fahrenheit (33 degrees Celsius) warmer than it should be, given the amount of sunlight reaching its surface. The best explanation for that discrepancy was that the atmosphere retained heat to warm the planet.

Tyndall and Foote showed that nitrogen and oxygen, which together account for 99 percent of the atmosphere, had essentially no influence on Earth's temperature because they did not absorb heat.

Rather, they found that gases present in much smaller concentrations were entirely responsible for maintaining temperatures that made the Earth habitable, by trapping heat to create a natural greenhouse effect.

A blanket in the atmosphere

Earth constantly receives energy from the Sun and radiates it back into space. For the planet's temperature to remain constant, the net heat it receives from the Sun must be balanced by outgoing heat that it gives off.

Since the Sun is hot, it gives off energy in the form of shortwave radiation at mainly ultraviolet and visible wavelengths. Earth is much cooler, so it emits heat as infrared radiation, which has longer wavelengths.

Carbon dioxide and other heat-trapping gases have molecular structures that enable them to absorb infrared radiation. The bonds between atoms in a molecule can vibrate in particular ways, like the pitch of a piano string. When the energy of a photon corresponds to the frequency of the molecule, it is absorbed and its energy transfers to the molecule.

Carbon dioxide and other heat-trapping gases have three or more atoms and frequencies that correspond to infrared radiation emitted by Earth. Oxygen and nitrogen, with just two atoms in their molecules, do not absorb infrared radiation.

Most incoming shortwave radiation from the Sun passes through the atmosphere without being absorbed.

But most outgoing infrared radiation is absorbed by heat-trapping gases in the atmosphere. Then they can release, or re-radiate, that heat. Some returns to Earth's surface, keeping it warmer than it would be otherwise.

Research on heat transmission

During the Cold War, the absorption of infrared radiation by many different gases was studied extensively. The work was led by the US Air Force, which was developing heat-seeking missiles and needed to understand how to detect heat passing through air.

This research enabled scientists to understand the climate and atmospheric composition of all planets in the Solar System by observing their infrared signatures. For example, Venus is about 870 F (470 C) because its thick atmosphere is 96.5 percent carbon dioxide.

It also informed weather forecast and climate models, allowing them to quantify how much infrared radiation is retained in the atmosphere and returned to Earth's surface.

People sometimes ask me why carbon dioxide is important for climate, given that water vapor absorbs more infrared radiation and the two gases absorb at several of the same wavelengths.

The reason is that Earth's upper atmosphere controls the radiation that escapes to space. The upper atmosphere is much less dense and contains much less water vapor than near the ground, which means that adding more carbon dioxide significantly influences how much infrared radiation escapes to space.

Observing the greenhouse effect

Have you ever noticed that deserts are often colder at night than forests, even if their average temperatures are the same? Without much water vapor in the atmosphere over deserts, the radiation they give off escapes readily to space.

In more humid regions radiation from the surface is trapped by water vapor in the air. Similarly, cloudy nights tend to be warmer than clear nights because more water vapor is present.

The influence of carbon dioxide can be seen in past changes in climate. Ice cores from over the past million years have shown that carbon dioxide concentrations were high during warm periods - about 0.028 percent.

During ice ages, when Earth was roughly 7 to 13 F (4-7 C) cooler than in the 20th century, carbon dioxide made up only about 0.018 percent of the atmosphere.

Even though water vapor is more important for the natural greenhouse effect, changes in carbon dioxide have driven past temperature changes. In contrast, water vapor levels in the atmosphere respond to temperature.

As Earth becomes warmer, its atmosphere can hold more water vapor, which amplifies the initial warming in a process called the "water vapor feedback." Variations in carbon dioxide have therefore been the controlling influence on past climate changes.

Small change, big effects

It shouldn't be surprising that a small amount of carbon dioxide in the atmosphere can have a big effect. We take pills that are a tiny fraction of our body mass and expect them to affect us.

Today the level of carbon dioxide is higher than at any time in human history. Scientists widely agree that Earth's average surface temperature has already increased by about 2 F (1 C) since the 1880s, and that human-caused increases in carbon dioxide and other heat-trapping gases are extremely likely to be responsible.

Without action to control emissions, carbon dioxide might reach 0.1 percent of the atmosphere by 2100, more than triple the level before the Industrial Revolution. This would be a faster change than transitions in Earth's past that had huge consequences.

Without action, this little sliver of the atmosphere will cause big problems.

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
Jason West, Professor of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill. This article is republished from The Conversation under a Creative Commons license. Read the original article.

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CO2 Makes Up Just 0.04% of Earth's Atmosphere. Here's Why Its Impact Is So Massive

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Reader question: I heard that carbon dioxide makes up 0.04 percent of the world's atmosphere. Not 0.4 percent or 4 percent, but 0.04 percent! How can it be so important in global warming if it's such a small percentage?

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Three-fourths of all air resides in the troposphere, the lowest layer of the Earth's atmosphere. Air is a mixture of gases, most of which are naturally occurring. Air also contains a significant amount of human-made air pollutants, including some that are not safe to breathe and some that warm our planet's climate. The troposphere also contains water in all three phases (liquid, solid, and gas) as well as solid particles called aerosols.

Gases

The most abundant naturally occurring gas is nitrogen (N ₂), which makes up about 78% of air. Oxygen (O ₂) is the second most abundant gas at about 21%. The inert gas argon (Ar) is the third most abundant gas at 0.93%. There are also trace amounts of carbon dioxide (CO ₂), neon (Ne), helium (He), methane (CH ₄), krypton (Kr), hydrogen (H ₂), nitrous oxide (NO), xenon (Xe), ozone (O ₃), iodine (I2), carbon monoxide (CO), and ammonia (NH ₃) in the atmosphere.

Water Vapor

Due to the water cycle, the amount of water in the air is constantly changing. The lower troposphere can contain up to 4% water vapor (H ₂O) in areas near the tropics, while the poles contain only trace amounts of water vapor. The concentration of water vapor decreases drastically with altitude. The upper troposphere has less water vapor than air near the surface, the stratosphere and mesosphere have almost no water vapor, and the thermosphere contains none at all.

Aerosols

Air also contains tiny solid particles called aerosols, such as dust, sea salt, and ash from erupting volcanoes or forest fires. Many of these particles are so small that they are microscopic. Others are large enough to see. Aerosols affect climate by helping clouds form and shading the planet by scattering or absorbing sunlight. In the last century, manufacturing and widespread use of combustion engines have increased the number of aerosols in the atmosphere as particulate matter spews from smokestacks and exhaust pipes. Burning wood and other materials also add particles to the air.

Atmospheric Chemistry

Like everything on Earth, the air is made of chemicals. The chemicals in the air often combine with each other, or with other chemicals from the Earth's surface, through chemical reactions. Many of these chemical reactions help maintain healthy natural environments and are vital for plants and animals. Nitrogen gas in the atmosphere does almost nothing, but nitrogen elsewhere on Earth is essential for life. Through the nitrogen cycle, nitrogen makes its way into soil and water, binds with other elements, and can be used by living things. Oxygen from the atmosphere causes oxidation reactions that help break down matter and release nutrients into soils, and is used by humans and animals in cellular respiration.

Atmospheric chemistry in the troposphere is also influenced by human-made chemicals that can negatively impact human health and the environment. For example:

Vehicle exhaust contains nitrogen dioxide, as well as other polluting chemicals such as carbon monoxide and sulfur dioxide. Nitrogen dioxide reacts with atmospheric oxygen to form tropospheric ozone which is hazardous to plant and animal cells.

Smog, which is mainly made of ozone and particulate carbon (soot) emitted by coal-burning power plants, causes damage to the lungs of humans and animals.

Factories that burn fossil fuels also release sulfur and nitrogen dioxides, which combine with water in the atmosphere to make acid rain. Acid rain causes damage to natural and human-made environments.

Chemistry of the Air

The table below lists the major gas components and their role in the atmosphere. Click on each molecule name to learn more about them.

Gas

Chemical & Molecular
Structure

Role in the Atmosphere

Nitrogen Oxides

Nitrogen oxides are air pollutants that contribute to the formation of ozone. They also create nitric acid when they mix with water droplets in the air, which is part of acid rain.

Argon

Argon makes up about 1% of the atmosphere and comes mostly from the decay of potassium in the Earth's crust. It is an inert gas, which means that it does not react with other chemicals.

Water Vapor

Water is cycled through all of Earth's systems in each of its three phases: solid, liquid, or gas. Water vapor in the atmosphere is a greenhouse gas due to its heat-trapping ability.

Sulfur Oxides

Sulfur oxides are produced when coal and oil are burned. It's also released from volcanoes. The sulfur oxides mix with water droplets in the atmosphere to create sulfuric acid, which is a component of acid rain.

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Three-fourths of all air resides in the troposphere, the lowest layer of the Earth's atmosphere. Air is a mixture of gases, most of which are naturally occurring. Air also contains a significant amount of human-made air pollutants, including some that are not safe to breathe and some that warm our planet's climate.

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How Much Carbon Dioxide Are We Emitting? - NASA Science

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A visualization feature captures the quantities of climate change.

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Indoor Carbon Dioxide Levels and Your Health | Indoor Doctor

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We need to talk about ventilation. Urgently. Specifically, policy-makers and industry need to arrive at an agreed definition of sufficiently ventilated when it comes to the indoor spaces where New Zealanders live, work, learn, play and train.

This really gave me pause for thought. Ventilation is a balancing act in a heating climate like New Zealand. One the one hand, we value the results of ventilation-fresher air and reduced humidity-and the health benefits. On the other hand, most indoor spaces in New Zealand are already inadequately heated in colder months and outside of a Passive House quality build, ventilating more increases heating demand as hot air is lost to outside.

Stumm's article starts by noting existing guides for ventilation use CO2 levels as a proxy for good indoor air quality. From many data points, industry has previously settled on indoor environments staying below 1000 ppm CO2. However, this number has been repeatedly revised and is now being debated anew. Several studies offer substantial evidence that extended exposure to even 1000 ppm of CO2 reduces people's ability to think clearly and make decisions [Allen 2015].

In a 2016 study in the US, when office ventilation was improved and levels of carbon dioxide and emissions reduced, employees performed 61% better on cognitive tasks compared to the standard office conditions. By further doubling the ventilation in the first setting, cognitive performance more than doubled.

What really made me reflect is the authors' point that CO2 levels outside continue to increase, ventilation alone may be unable to keep indoor CO2 levels at optimal levels. The theoretical solutions sound like something out of a science fiction novel: spacecraft CO2 scrubbers and oxygen enrichment. This dystopian vision aside, we need to design buildings for better ventilation rates . Retrofitting to increase ventilation is expensive and complicated, especially in large buildings. Let's stop building things we need to fix.

NIWA continuously records CO2 levels at Baring Head. Its clean air station has been running since 1972 and is home to the longest running continuous CO2 measurements in the southern hemisphere. This graph is frankly horrifying.

If we go on with intensive use of hydrocarbon fuels, climate models predict CO2 levels could reach close to 1000 ppm by 2100. That means not only an unhinged climate but significant reductions in humans' cognition and decision-making abilities, even in 'fresh' air. Compounding that, our cities have higher CO2 levels than Baring Head because of the pollution and number of people concentrated there, so we'd hit the higher levels sooner than later.

References

Studies showing significant reductions in cognition and decision-making abilities include the following.

The 1000 ppm by 2100 references are here.

IPCC. 2000. " Emissions Scenarios ." Special Report of Intergovernmental Panel on Climate Change Working Group III, published for the IPCC.

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Optimal indoor CO2 levels: is 1000ppm too high? - Sustainable Engineering Ltd.

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We need to talk about ventilation. Urgently. Specifically, policy-makers and industry need to arrive at an agreed definition of sufficiently ventilated when it comes to the indoor spaces where New Zealanders live, work, learn, play and train. CO2 levels are a useful measure of indoor air quality.

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what is the average co2 levels inside my house

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what is the average co2 levels inside my house

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When it comes to ensuring a safe and healthy indoor environment for your family, one often overlooked factor is the level of carbon dioxide (CO2) in your home. Many of us are aware of the importance of proper ventilation and air quality, but understanding what constitutes an unhealthy CO2 level is equally crucial. In this beginner's guide, we'll delve into the recommended CO2 levels for indoor spaces, the health effects of high CO2 levels, how to measure CO2 levels, and what you can do to reduce them.

What is the Recommended CO2 Level for Indoor Spaces?

CO2 is a naturally occurring gas that is the main source of carbon to support all life on earth. While it is a necessary component of a healthy ecosystem, carbon dioxide can negatively impact human health when it is present in higher than normal concentrations.

The recommended CO2 level for healthy indoor spaces typically falls within the range of 350 to 1,000 parts per million (ppm). However, it's essential to note that the specific recommended levels can vary depending on the purpose of the space. Here's a breakdown of typical CO2 levels:

350-450 ppm: Ideal CO2 levels for well-ventilated outdoor air.

450-600 ppm: Excellent indoor air quality with ample ventilation.

600-1,000 ppm: Acceptable levels for most indoor spaces but may indicate a need for increased ventilation.

Above 1,000 ppm: Elevated CO2 levels that may lead to health concerns if sustained.

These recommendations are established to ensure a healthy and comfortable indoor environment, as elevated CO2 levels can have adverse effects on our well-being.

Source: https://www.co2meter.com/en-es/blogs/news/co2-levels-at-home-tester

What Are the Health Effects of High CO2 Levels?

Exposure to high CO2 levels can lead to a range of health issues, particularly when those levels persist over time. Some common health effects associated with elevated CO2 levels include:

Headaches: Increased CO2 can lead to headaches, dizziness, and a feeling of discomfort.

Fatigue: High CO2 levels can make you feel tired and sluggish, reducing productivity.

Reduced Cognitive Function: Prolonged exposure to elevated CO2 levels may impair cognitive function and decision-making.

Shortness of Breath: Breathing can become more challenging in areas with excessive CO2.

Irritation: Irritated eyes, nose, and throat can occur, resembling allergy symptoms.

Long-Term Health Risks: Chronic exposure to high CO2 levels may contribute to respiratory conditions and cardiovascular problems.

To ensure the well-being of your family, it's crucial to monitor and control CO2 levels in your living spaces.

Source: https://www.nature.com/articles/s41893-019-0323-1.epdf

How Can I Measure CO2 Levels in My Home or Office?

Measuring CO2 levels in your home or office is a straightforward process thanks to modern technology. You can use a CO2 monitor or detector to get an accurate reading of the CO2 concentration in the air. Here's how you can do it:

1. Purchase an and other indoor IAQ Device by Sensables.io to Monitor CO2 air pollutants.

2. Set up alerts through the easy monitoring through your phone.

3. Place the Monitor Strategically: Position the monitor in a central location within the room, away from windows, doors, and vents.

4. Monitor and Interpret Readings: Regularly check the monitor's readings through your smartphone and use alerts. If the levels consistently exceed the recommended range, it's time to take action.

What Can I Do to Reduce CO2 Levels in My Home or Office?

Maintaining proper ventilation is the key to reducing CO2 levels in indoor spaces. Here are some effective strategies to help you achieve this:

Open Windows and Doors: Whenever possible, allow fresh outdoor air to circulate through your home or office.

Use Exhaust Fans: In areas like kitchens and bathrooms, use exhaust fans to expel indoor air laden with CO2.

Invest in Air Purifiers: High-quality air purifiers can help remove CO2 and other pollutants from the air.

: Certain indoor plants, like snake plants and peace lilies, can naturally help reduce CO2 levels by absorbing carbon dioxide and releasing oxygen.

Limit Indoor Activities: Minimize activities that generate CO2 indoors, such as excessive use of gas stoves or fireplaces.

Visit a Clean Air Center: In times of extreme indoor air quality issues, some cities and municipalities offer clean air centers that are open to the public.

Frequently Asked Questions

What CO2 level is dangerous?

A CO2 level consistently above 1,000 ppm is considered dangerous and can lead to health issues if not addressed.

Is CO2 a pollutant?

No, carbon dioxide is not a pollutant. In fact, CO2 is necessary to sustain all life on earth. However, CO2 levels can increase to unhealthy levels in poorly ventilated spaces due to various activities. It's important to manage CO2 levels to prevent too much exposure over long periods of time.

Can high CO2 levels be harmful to children?

Yes, high CO2 levels can be harmful to children, just as they are to adults. Children may be more sensitive to changes in indoor air quality.

Does high CO2 indoors create an economic burden on society?

Research shows high levels of CO2 in indoor spaces can reduce the amount of oxygen available for brain function, which contributes to decreased alertness and productivity. Better management of pollutants such as CO2 could create massive economic benefits for society as a whole.

Are there government guidelines for indoor CO2 levels?

Yes, various government agencies, such as the Environmental Protection Agency (EPA), provide guidelines for indoor CO2 levels to ensure a healthy living environment.

Can I use indoor plants to reduce CO2 levels?

Yes, certain indoor plants can help reduce CO2 levels by absorbing carbon dioxide during photosynthesis.

Do I need a professional to measure CO2 levels in my home?

While it's not necessary to hire a professional to measure CO2 levels, using a reliable CO2 monitor is recommended for accurate readings.

Maintaining Healthy CO2 Indoors

Maintaining or home is essential for the well-being of your family and yourself. By following the recommended guidelines, regularly monitoring CO2 levels, and implementing effective ventilation strategies, you can ensure a safe and healthy indoor environment. Don't underestimate the acceptable levels of CO2 in your office importance of indoor air quality, as it plays a significant role in your overall health and comfort.

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Acceptable Levels of CO2 in Your Home: What Is Safe? - YourIAQ

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Learn the acceptable levels of CO2 in your home and how you can measure and reduce potentially harmful CO2 for better indoor air quality.

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ppm stands for Parts Per Millon and that's how I measure my co2 levels for example there is 114ppm in my room.

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New Zealand: Per capita: how much CO₂ does the average person emit?

Annual emissions figures are often used to compare countries' contribution to climate change. But this metric often reflects differences in population size across the world.

To understand the 'footprint' of the average person in a given country, this chart shows per capita emissions.

These figures reflect 'production-based' emissions, so do not correct for traded goods.

Two tips on how you can interact with this chart

New Zealand: What are the country's annual CO₂ emissions?

This interactive chart shows how much carbon dioxide (CO ₂) is produced in a given year.

A few points to keep in mind when considering this data:

These figures are based on 'production' or 'territorial' emissions (i.e. emissions from the burning of fossil fuels, or cement production within a country's borders). It does not consider the emissions of traded goods (consumption-based emissions). You find consumption-based emissions later in this country profile.

These figures look specifically at CO₂ emissions - not total greenhouse gas emissions. You find total, and other greenhouse gas emissions, later in this country profile.

Annual emissions can be largely influenced by population size - we present the per capita figures above.

New Zealand: Year-on-year change: what is the percentage change in CO₂ emissions?

This interactive chart shows the year-on-year growth in annual CO ₂ emissions.

A positive figure indicates that the emissions in a given year were higher than the previous year.

A negative figure indicates that emissions were lower than the previous year.

Year-to-year changes in emissions can vary a lot - this can create a particularly 'noisy' time series.

When we only look at emissions produced today, we fail to recognise historical responsibility for emissions in recent decades or centuries.

This interactive chart shows cumulative CO ₂ emissions - the sum of emissions produced since 1751 to the given year. This allows us to understand how much of the total CO ₂ emissions to date has been emitted by a given country.

New Zealand: Consumption-based accounting: how do emissions compare when we adjust for trade?

When countries set targets, measure or compare CO ₂ emissions, they tend to focus on production-based emissions - CO ₂ emitted within a country's own borders. However, this fails to capture emissions from traded goods - the CO ₂ emitted in the production of goods elsewhere, which are later imported (or the opposite: emissions from goods that are exported).

We can estimate consumption-based CO ₂ emissions by correcting for trade. These emissions are shown in the interactive chart. Note that the resolution of data needed to calculate this is not available for all countries.

→ We provide more detail on consumption-based emissions in our article ' How do CO2 emissions compare when we adjust for trade? '

Looking at a country's annual emissions is useful, but it can be hard to put these numbers in context of the global total. Is 10 million tonnes of CO ₂ large or small; what about 100 million; or 1 billion tonnes?

This interactive chart shows annual emissions as a percentage of the global total in a given year.

Just as with annual emissions, simply presenting cumulative CO ₂ figures can be hard to contextualize. Has a given country's contribution to the global total been large or small?

This chart shows the country's cumulative emissions as a share of global cumulative emissions.

Coal, oil, gas, cement: how much does each contribute to CO₂ emissions?

CO ₂ emissions are dominated by the burning of fossil fuels for energy production, and industrial production of materials such as cement.

What is the contribution of each fuel source to the country's CO ₂ emissions?

This interactive chart shows the breakdown of annual CO ₂ emissions by source: either coal, oil, gas, cement production or gas flaring. This breakdown is strongly influenced by the energy mix of a given country, and changes as a country shifts to or from a given energy source.

How you can interact with this chart

New Zealand: How are CO₂ emissions from different fuels changing?

The chart above allows us to see the breakdown of CO ₂ emissions by fuel type. But it makes it more difficult to see the absolute change in particular fuel sources over time.

This interactive chart shows the same data - CO ₂ emissions from coal, oil, gas, cement and flaring - but as individual lines to see clearly how each is changing over time.

In discussions on climate change, we tend to focus on carbon dioxide (CO ₂) - the most dominant greenhouse gas produced by the burning of fossil fuels, industrial production, and land use change.

But CO ₂ is not the only greenhouse gas that is driving global climate change. There are a number of others - methane, nitrous oxide, and trace gases such as the group of 'F-gases' - which have contributed a significant amount of warming to date.

Here we look at total greenhouse gas (GHG) emissions across the world, plus breakdowns of other major gases including methane and nitrous oxide.

New Zealand: Total greenhouse gas emissions: how much does the average person emit? Where do emissions come from?

The charts above focused on carbon dioxide (CO ₂). But CO ₂ is not the only greenhouse gas. Others, including methane and nitrous oxide, have also had a significant impact on global warming to date.

The first interactive chart shows per capita greenhouse gas emissions. This is measured as the sum of all greenhouse gases, and given by a metric called 'carbon dioxide equivalents'.

'Carbon dioxide equivalents' try to correct for the fact that one unit (e.g. a tonne) of a given gas doesn't have the same same impact on warming as another. We therefore multiply the emissions of each gas by its 'global warming potential' (GWP) value: this measures the amount of warming one tonne of that gas would create relative to one tonne of CO ₂.

The other interactive chart shows where these emissions come from: the contribution of each sector.

→ We provide more detail on total greenhouse gas emissions in our sub-page ' Greenhouse gas emissions '.

New Zealand: Methane: how much does the average person emit? Where do emissions come from?

Methane (CH ₄) is a strong greenhouse gas, mainly produced through agricultural activities (e.g. livestock and rice production), in addition to leakages from oil and gas production (called 'fugitive emissions').

This first interactive chart here shows per capita emissions of methane each year. This is measured in 'carbon dioxide equivalents'.

The other interactive chart shows where these emissions come from: the contribution of each sector.

→ We look at the breakdown of methane sources in our sub-page ' Emissions by sector '.

New Zealand: Nitrous oxide: how much does the average person emit? Where do emissions come from?

Nitrous oxide (N ₂ O) is a strong greenhouse gas, that is mainly produced from agricultural activities (e.g. from the use of synthetic and organic fertilizers to grow crops).

This first interactive chart here shows per capita emissions of nitrous oxide each year. This is measured in 'carbon dioxide equivalents'.

The other interactive chart shows where these emissions come from: the contribution of each sector.

→ We look at the breakdown of nitrous oxide sources in our sub-page ' Emissions by sector '.

New Zealand: Energy intensity: how much energy does it use per unit of GDP?

Since energy is such a large contributor to CO ₂, reducing energy consumption can inevitably help to reduce emissions. However, some energy consumption is essential to human wellbeing and rising living standards.

Energy intensity can therefore be a useful metric to monitor. Energy intensity measures the amount of energy consumed per unit of gross domestic product. It effectively measures how efficiently a country uses energy to produce a given amount of economic output. A lower energy intensity means it needs less energy per unit of GDP.

This interactive chart shows energy intensity.

Two tips on how you can interact with this chart

New Zealand: Carbon intensity: how much carbon does it emit per unit of energy?

Energy intensity - shown in the chart above - is one important metric to monitor whether countries are making progress in reducing emissions. The other key part of this equation is carbon intensity: the amount of CO ₂ emitted per unit of energy.

We can reduce emissions by (1) using less energy; and/or (2) using lower-carbon energy.

This metric monitors the second option. As we transition our energy mix towards lower-carbon sources (such as renewables or nuclear energy), the amount of carbon we emit per unit of energy should fall.

This chart shows carbon intensity - measured in kilograms of CO ₂ emitted per kilogram of oil equivalent consumed.

New Zealand: Has economic growth decoupled from CO₂ emissions?

To reduce emissions and achieve increasing prosperity at the same time, we have to decouple economic growth from CO ₂ emissions. Several countries have achieved this in recent years.

The chart here shows whether this country has achieved this by showing the change in GDP per capita, and annual per capita CO ₂ emissions over time.

We show both production-based and consumption-based emissions (for countries where this data is available). This allows us to see whether the import of production from other countries - or the export to other countries - has affected this change in emissions.

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Annual emissions figures are often used to compare countries' contribution to climate change. But this metric often reflects differences in population size across the world. To understand the 'footprint' of the average person in a given country, this chart shows per capita emissions. These figures reflect 'production-based' emissions, so do not correct for traded goods.

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Because plants use carbon dioxide to grow, it's tempting to think they might prefer a planet with more atmospheric CO₂ than is present today. That's not necessarily so.

It's true that plants love CO ₂. During photosynthesis, they take in carbon dioxide and, with the assistance of water and sunlight, make energy for themselves while releasing oxygen for us to breathe. Plants have been around for billions of years and have lived on Earth at times when the planet had far more CO ₂ in the air than it does now. So, would plants prefer a more carbon-heavy planet, like the one humans are now creating with our greenhouse gas emissions?

Not necessarily, says David Des Marais, an MIT Professor of Civil and Environmental Engineering who studies how plants respond to their environments. "The short answer," Des Marais says, "is that most plants will grow faster and bigger with extra atmospheric CO ₂-all else being equal." However, plant growth is too complex for a one-size-fits-all law like "more CO ₂ is better."

Experiments in which scientists piped extra CO ₂ into plant-growing chambers have proven this basic science: the additional carbon makes plants grow faster if you maintain other factors, such as soil nutrient and water availability. ¹ Yet things may not be so simple for the planet at large, Des Marais says. Additional experiments have tracked plants growing in free air carbon enrichment (FACE) sites, where the researchers added CO ₂ not to enclosed chambers but to open environments such as agricultural fields that more closely simulate reality. Although the added carbon sped up plant growth in these places, it did not accelerate nearly as quickly as for plants in closed, CO ₂-rich chambers. ²

Although plants need carbon dioxide to grow, their success in very high-carbon environments is not guaranteed. Not all plants like extra carbon equally. And for those carbon aficionados in the plant kingdom, CO ₂ is not the only factor that controls growth. As any aspiring green thumb knows, plants need the right balance of water and soil nutrients to translate extra carbon dioxide into growth.

This is a problem, given the way our climate is trending. Climate change, driven by excessive CO ₂ in the atmosphere, deepens droughts in places like the American West. That reduces the water supply for plants there while simultaneously increasing the risk of catastrophic wildfires. In other places, plants will have to cope with more frequent disasters like flooding and heat stress, exposure to saltwater from rising seas, and an increase in pests that enjoy warmer winters.

And though planting millions of additional trees is one popular idea often floated for pulling some CO ₂ out of the atmosphere, it is not clear that the world would have enough nutrients in the soil to allow for such growth.

That's bad news for plants, and for people hoping for some relief from climate change. So is the fact that the process of respiration, when plants release some of their stored CO ₂, happens faster under hotter conditions. "That's the real devil in a lot of these carbon sequestration conversations," Des Marais says. "It's one thing to get the carbon out of the air and into the trees or soil, but it has to stay there. And if you increase temperature, you tend to increase respiration."

Des Marais says some people point to climates of deep history as proof that plants can endure or even enjoy very high concentrations of carbon in the air. We know from the geologic record that hundreds of millions of years ago, Earth had an atmospheric CO ₂ level in excess of 2,000 parts per million (ppm). That's compared to around 280 ppm in pre-industrial times and 417 ppm in 2022. ³

Although plenty of plants lived through that period-albeit different species and in different places than today-humans did not. Such a CO ₂ level would produce year-round scorching temperatures akin to what we experience in summer today. In other words, he says, "this is not a period we would ever want to visit."
Thank you to José Rodriguez of Cuernavaca, Morelos, Mexico, for the question. You can submit your own question to Ask MIT Climate Read more Ask MIT Climate .

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Don't plants do better in environments with very high CO2?

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Because plants use carbon dioxide to grow, it's tempting to think they might prefer a planet with more atmospheric CO2 than is present today. That's not necessarily so.

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The alarming rate of carbon dioxide flowing into our atmosphere is affecting plant life in interesting ways - but perhaps not in the way you'd expect.

Despite large losses of vegetation to land clearing, drought and wildfires, carbon dioxide is absorbed and stored in vegetation and soils at a growing rate.

This is called the "land carbon sink", a term describing how vegetation and soils around the world absorb more carbon dioxide from photosynthesis than they release. And over the past 50 years, the sink (the difference between uptake and release of carbon dioxide by those plants) has been increasing, absorbing at least a quarter of human emissions in an average year.

The sink is getting larger because of a rapid increase in plant photosynthesis, and our new research shows rising carbon dioxide concentrations largely drive this increase.

So, to put it simply, humans are producing more carbon dioxide. This carbon dioxide is causing more plant growth, and a higher capacity to suck up carbon dioxide. This process is called the "carbon dioxide fertilisation effect" - a phenomenon when carbon emissions boost photosynthesis and, in turn, plant growth.

What we didn't know until our study is just how much the carbon dioxide fertilisation effect contributes to the increase in global photosynthesis on land.

But don't get confused, our discovery doesn't mean emitting carbon dioxide is a good thing and we should pump out more carbon dioxide, or that land-based ecosystems are removing more carbon dioxide emissions than we previously thought (we already know how much this is from scientific measurements).

And it definitely doesn't mean mean we should, as climate sceptics have done, use the concept of carbon dioxide fertilisation to downplay the severity of climate change.

Read more: How to design a forest fit to heal the planet

Rather, our findings provide a new and clearer explanation of what causes vegetation around the world to absorb more carbon than it releases.

What's more, we highlight the capacity of vegetation to absorb a proportion of human emissions, slowing the rate of climate change. This underscores the urgency to protect and restore terrestrial ecosystems like forests, savannas and grasslands and secure their carbon stocks.

And while more carbon dioxide in the atmosphere does allow landscapes to absorb more carbon dioxide, almost half (44%) of our emissions remain in the atmosphere.

More carbon dioxide makes plants more efficient

Since the beginning of the last century, photosynthesis on a global scale has increased in nearly constant proportion to the rise in atmospheric carbon dioxide. Both are now around 30% higher than in the 19th century, before industrialisation began to generate significant emissions.

Carbon dioxide fertilisation is responsible for at least 80% of this increase in photosynthesis. Most of the rest is attributed to a longer growing season in the rapidly warming boreal forest and Arctic.

So how does more carbon dioxide lead to more plant growth anyway?

Higher concentrations of carbon dioxide make plants more productive because photosynthesis relies on using the sun's energy to synthesise sugar out of carbon dioxide and water. Plants and ecosystems use the sugar both as an energy source and as the basic building block for growth.

When the concentration of carbon dioxide in the air outside a plant leaf goes up, it can be taken up faster, super-charging the rate of photosynthesis.

Read more: CO₂ levels and climate change: is there really a controversy?

More carbon dioxide also means water savings for plants. More carbon dioxide available means pores on the surface of plant leaves regulating evaporation (called the stomata) can close slightly. They still absorb the same amount or more of carbon dioxide, but lose less water.

The resulting water savings can benefit vegetation in semi-arid landscapes that dominate much of Australia.

We saw this happen in a 2013 study, which analysed satellite data measuring changes in the overall greenness of Australia. It showed more leaf area in places where the amount of rain hadn't changed over time. This suggests water efficiency of plants increases in a carbon dioxide-richer world.

Young forests help to capture carbon dioxide

In other research published recently, we mapped the carbon uptake of forests of different ages around the world. We showed forests regrowing on abandoned agricultural land occupy a larger area, and draw down even more carbon dioxide than old-growth forests, globally. But why?

In a mature forest, the death of old trees balances the amount of new wood grown each year. The old trees lose their wood to the soil and, eventually, to the atmosphere through decomposition.

A regrowing forest, on the other hand, is still accumulating wood, and that means it can act as a considerable sink for carbon until tree mortality and decomposition catch up with the rate of growth.

Read more: Forest thinning is controversial, but it shouldn't be ruled out for managing bushfires

This age effect is superimposed on the carbon dioxide fertilisation effect, making young forests potentially very strong sinks.

In fact, globally, we found such regrowing forests are responsible for around 60% of the total carbon dioxide removal by forests overall. Their expansion by reforestation should be encouraged.

Forests are important to society for so many reasons - biodiversity, mental health, recreation, water resources. By absorbing emissions they are also part of our available arsenal to combat climate change. It's vital we protect them.

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Yes, more carbon dioxide in the atmosphere helps plants grow, but it's no excuse to downplay climate change

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The alarming rate of carbon dioxide flowing into our atmosphere is affecting plant life in interesting ways - but perhaps not in the way you'd expect. Despite large losses of vegetation to land clearing, drought and wildfires, carbon dioxide is absorbed and stored in vegetation and soils at a growing rate.

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Atmospheric concentrations of carbon dioxide have been steadily rising, from approximately 315 ppm (parts per million) in 1959 to a current atmospheric average of approximately 385 ppm (Keeling et al.,2009). Current projections are for concentrations to continue to rise to as much as 500-1000 ppm by the year 2100 (IPCC 2007).

While a great deal of media and public attention has focused on the effects that such higher concentrations of CO ₂ are likely to have on global climate, rising CO ₂ concentrations are also likely to have profound direct effects on the growth, physiology, and chemistry of plants, independent of any effects on climate (Ziska 2008). These effects result from the central importance of CO ₂ to plant metabolism. As photosynthetic organisms, plants take up atmospheric CO ₂, chemically reducing the carbon. This represents not only an acquisition of stored chemical energy for the plant, but also provides the carbon skeletons for the organic molecules that make up a plants' structure. Overall, the carbon, hydrogen and oxygen assimilated into organic molecules by photosynthesis make up ~96% of the total dry mass of a typical plant (Marschner 1995). Photosynthesis is therefore at the heart of the nutritional metabolism of plants, and increasing the availability of CO ₂ for photosynthesis can have profound effects on plant growth and many aspects of plant physiology.

Our knowledge of plant responses to future CO ₂ concentrations rests on the results of experiments that have experimentally increased CO ₂ and then compared the performance of the experimental plants with those grown under current ambient CO ₂ conditions. Such experiments have been performed in a wide variety of settings, including greenhouses and chambers of a variety of sizes and designs. However plants grown in chambers may not experience the effects of increasing CO ₂ the same way as plants growing in more natural settings. For this reason, techniques of Free-Air Carbon dioxide Enrichment (FACE) have been developed that allow natural or agricultural ecosystems to be fumigated with elevated concentrations of CO ₂ in the field without use of chambers (Figure 1). As these experiments are the most naturalistic, they should provide the best indication of the responses of plants to increased CO ₂ under the real-world conditions of the future. This article therefore focuses on data from FACE experiments wherever these are available. Whenever possible, to ensure the generality of conclusions, reference is made to analyses that have incorporated data from multiple experiments independently conducted at various research facilities.

One of the most consistent effects of elevated atmospheric CO ₂ on plants is an increase in the rate of photosynthetic carbon fixation by leaves. Across a range of FACE experiments, with a variety of plant species, growth of plants at elevated CO ₂ concentrations of 475-600 ppm increases leaf photosynthetic rates by an average of 40% (Ainsworth & Rogers 2007). Carbon dioxide concentrations are also important in regulating the openness of stomata, pores through which plants exchange gasses, with the external environment. Open stomata allow CO ₂ to diffuse into leaves for photosynthesis, but also provide a pathway for water to diffuse out of leaves. Plants therefore regulate the degree of stomatal opening (related to a measure known as stomatal conductance) as a compromise between the goals of maintaining high rates of photosynthesis and low rates of water loss. As CO ₂ concentrations increase, plants can maintain high photosynthetic rates with relatively low stomatal conductance. Across a variety of FACE experiments, growth under elevated CO ₂ decreases stomatal conductance of water by an average of 22% (Ainsworth & Rogers 2007). This would be expected to decrease overall plant water use, although the magnitude of the overall effect of CO ₂ will depend on how it affects other determinants of plant water use, such as plant size, morphology, and leaf temperature. Overall, FACE experiments show decreases in whole plant water use of 5-20% under elevated CO ₂. This in turn can have consequences for the hydrological cycle of entire ecosystems, with soil moisture levels and runoff both increasing under elevated CO ₂ (Leakey et al. 2009).

Since photosynthesis and stomatal behavior are central to plant carbon and water metabolism, growth of plants under elevated CO ₂ leads to a large variety of secondary effects on plant physiology. The availability of additional photosynthate enables most plants to grow faster under elevated CO ₂, with dry matter production in FACE experiments being increased on average by 17% for the aboveground, and more than 30% for the belowground, portions of plants (Ainsworth & Long 2005; de Graaff et al. 2006). This increased growth is also reflected in the harvestable yield of crops, with wheat, rice and soybean all showing increases in yield of 12-14% under elevated CO ₂ in FACE experiments (Ainsworth 2008; Long et al. 2006).

Elevated CO ₂ also leads to changes in the chemical composition of plant tissues. Due to increased photosynthetic activity, leaf nonstructural carbohydrates (sugars and starches) per unit leaf area increase on average by 30-40% under FACE elevated CO ₂ (Ainsworth 2008; Ainsworth & Long 2005). Leaf nitrogen concentrations in plant tissues typically decrease in FACE under elevated CO ₂, with nitrogen per unit leaf mass decreasing on average by 13% (Ainsworth & Long 2005). This decrease in tissue nitrogen is likely due to several factors: dilution of nitrogen from increased carbohydrate concentrations; decreased uptake of minerals from the soil, as stomatal conductance decreases and plants take up less water (Taub & Wang 2008); and decreases in the rate of assimilation of nitrate into organic compounds (Bloom et al. 2010).

Protein concentrations in plant tissues are closely tied to plant nitrogen status. Changes in plant tissue nitrogen are therefore likely to have important effects on species at higher trophic levels. Performance is typically diminished for insect herbivores feeding on plants grown in elevated CO ₂ (Zvereva & Kozlov 2006). This can lead to increased consumption of plant tissues as herbivores compensate for decreased food quality (Stiling and Cornelissen 2007). Effects on human nutrition are likely as well. In FACE experiments, protein concentrations in grains of wheat, rice and barley, and in potato tubers, are decreased by 5-14% under elevated CO ₂ (Taub et al. 2008). Crop concentrations of nutritionally important minerals including calcium, magnesium and phosphorus may also be decreased under elevated CO ₂ (Loladze 2002; Taub & Wang 2008).

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Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants

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Atmospheric concentrations of carbon dioxide have been steadily rising, from approximately 315 ppm (parts per million) in 1959 to a current atmospheric average of approximately 385 ppm (Keeling et al.,2009). Current projections are for concentrations to continue to rise to as much as 500-1000 ppm by the year 2100 (IPCC 2007).

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The greenhouse effect happens when certain gases, which are known as greenhouse gases, accumulate in Earth's atmosphere. Greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and fluorinated gases.

Greenhouse gases allow the sun's light to shine onto Earth's surface, and then the gases, such as ozone, trap the heat that reflects back from the surface inside Earth's atmosphere. The gases act like the glass walls of a greenhouse-thus the name, greenhouse gas.

According to scientists, the average temperature of Earth would drop from 14˚C (57˚F) to as low as -18˚C (-0.4˚F), without the greenhouse effect.

Some greenhouse gases come from natural sources, for example, evaporation adds water vapor to the atmosphere. Animals and plants release carbon dioxide when they respire, or breathe. Methane is released naturally from decomposition. There is evidence that suggests methane is released in low-oxygen environments, such as swamps or landfills. Volcanoes-both on land and under the ocean-release greenhouse gases, so periods of high volcanic activity tend to be warmer.

Since the Industrial Revolution of the late 1700s and early 1800s, people have been releasing larger quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of CO2, rose by about 80 percent during that time.

The amount of CO2 in the atmosphere far exceeds the naturally occurring range seen during the last 650,000 years.

Most of the CO2 that people put into the atmosphere comes from burning fossil fuels. Cars, trucks, trains, and planes all burn fossil fuels. Many electric power plants do as well. Another way humans release CO2 into the atmosphere is by cutting down forests, because trees contain large amounts of carbon.

People add methane to the atmosphere through livestock farming, landfills, and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agriculture and fossil fuel burning. Fluorinated gases include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). They are produced during the manufacturing of refrigeration and cooling products and through aerosols.

All of these human activities add greenhouse gases to the atmosphere. As the level of these gases rises, so does the temperature of Earth. The rise in Earth's average temperature contributed to by human activity is known as global warming.

The Greenhouse Effect and Climate Change

Even slight increases in average global temperatures can have huge effects.

Perhaps the biggest, most obvious effect is that glaciers and ice caps melt faster than usual. The meltwater drains into the oceans, causing sea levels to rise.

Glaciers and ice caps cover about 10 percent of the world's landmasses. They hold between 70 and 75 percent of the world's freshwater. If all of this ice melted, sea levels would rise by about 70 meters (230 feet).

The Intergovernmental Panel on Climate Change states that the global sea level rose about 1.8 millimeters (0.07 inches) per year from 1961 to 1993, and about 3.1 millimeters (0.12 inches) per year since 1993.

Rising sea levels cause flooding in coastal cities, which could displace millions of people in low-lying areas such as Bangladesh, the U.S. state of Florida, and the Netherlands.

Millions more people in countries like Bolivia, Peru, and India depend on glacial meltwater for drinking, irrigation, and hydroelectric power. Rapid loss of these glaciers would devastate those countries.

Greenhouse gas emissions affect more than just temperature. Another effect involves changes in precipitation, such as rain and snow.

Over the course of the 20th century, precipitation increased in eastern parts of North and South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa, the Mediterranean, and southern Asia.

As climates change, so do the habitats for living things. Animals that are adapted to a certain climate may become threatened. Many human societies depend on predictable rain patterns in order to grow specific crops for food, clothing, and trade. If the climate of an area changes, the people who live there may no longer be able to grow the crops they depend on for survival. Some scientists also worry that tropical diseases will expand their ranges into what are now more temperate regions if the temperatures of those areas increase.

Most climate scientists agree that we must reduce the amount of greenhouse gases released into the atmosphere. Ways to do this, include:

driving less, using public transportation, carpooling, walking, or riding a bike.

flying less-airplanes produce huge amounts of greenhouse gas emissions.

reducing, reusing, and recycling.

planting a tree-trees absorb carbon dioxide, keeping it out of the atmosphere.

using less electricity.

eating less meat-cows are one of the biggest methane producers.

supporting alternative energy sources that don't burn fossil fuels.

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The Greenhouse Effect and our Planet | National Geographic Society

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The greenhouse effect happens when certain gases, which are known as greenhouse gases, accumulate in Earth's atmosphere. Greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and fluorinated gases. Greenhouse gases allow the sun's light to shine onto Earth's surface, and then the gases, such as ozone, trap the heat that reflects back from the surface inside Earth's atmosphere.

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Are there fights over window openings and thermostat settings? Do customer HR managers ask about office CO2 levels? Can you improve ventilation in your meeting rooms?

Ventilation counteracts the spread of viruses within a room. But how can you know if your building ventilation is adequate?

Why it's important to measure CO2
CO2 level, as measured in parts-per-million, is our proxy for ventilation performance. Humans breathe out a lot of CO2 and if we see levels significantly increasing, then the ventilation is not coping. Time to turn up the fans, open windows, or remove bodies from the office.

Consider a meeting room of 250 sqft (25sqm) that has no ventilation at all. In just one hour, 4 occupants will breathe out enough CO2 such that the room exceeds the UK's HSE advisory limit (see table).

CO2 doesn't tell the whole picture, though. Temperature, humidity, and whether doors and windows are open or closed, contribute further knowledge to help you manage the space and take the right action.

Sensors provide data
This is where sensors come in. Modern sensors, connected to the cloud, are part of emerging IoT and Smart Building developments. Sensors are now being deployed in their millions, forcing costs down.

Equally, the range of what can now be measured is huge - not just for wellbeing but environmental performance, energy cost reporting, air pollution, or sensors for operations measuring anything from desk occupancy to cleaning supplies. Often a single device contains 5 or more sensors.

Once our data gets to the cloud, we can graph it dashboards, set KPIs and alert levels for interventions. We can even drop the data into our management software or occupier apps to communicate building performance.

Sensors produce a timeline of measurements that documents the internal environment. It is this data that tells management when to act or used to reassure customers.
LoRaWan - The New Sensor Network Technology
There is a new generation of sensors is based on a technology called LoRaWan. The sensors need no wires but run for years on simple consumer batteries. LoRa wireless can travel over a kilometre until its signals are picked up by low-cost LoRa gateways. The job of the gateway is to aggregate data from all deployed sensors for on-transmission to the cloud, where it is accessed and manipulated.

Better still, this technology is easily customised to meet specific demands from customers.

You can source "sensors as a service" from a good number of specialist providers. Or, with a little help, you can save cost by building your own, DIY, network.

In the case of CO2 and ventilation, these sensors enable you to build a distinctive message that associates wellbeing with your brand values.
Tony Freeth Informational (TFI) is a consultancy that assists Operators develop their technology base. We are organising sensor pilot studies and welcome new participants. Contact us on info@freeth.info for further information and a copy of the presentation made by Tony Freeth at the Flexsa Roundtable.

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Ventilation and CO2 - Making Measurements that Manage Wellbeing - Flexible Space Association

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Ventilation counteracts the spread of viruses within a room. But how can you know if your building ventilation is adequate?

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The New Brunswick legislature recently passed a motion to improve indoor air quality in the province's public buildings " to reduce the spread of airborne illnesses, such as COVID-19."

There are many ways to improve the air we breathe indoors, including filtration and ventilation: bring fresh air in, send exhaled air and contaminants out. And we have good reasons for looking at indoor air quality.

From wildfire smoke, to industrial pollution, many of us have felt the impacts of poor air quality and turned to air filters and respirators to cope.

The White House held a summit last year on improving indoor air quality to reduce the transmission of COVID-19. This September, there will be a similar meeting in Europe organized by the World Health Organization.

How new is all this? Well, it is and it isn't. Eighteenth-century physicians were big advocates for ventilation as a way of reducing the transmission of contagious diseases, though not entirely for sound reasons.

Ventilation and eighteenth-century medicine

I teach about eighteenth-century literature and medical writing in the British Isles. In the 1700s, British physicians took advantage of new scientific approaches but had little technology to see what was going on.

They believed that most contagious illnesses spread through smelly decaying matter, or miasma, from rotting food, sick bodies and so on. This is called " miasma theory," and it was eventually replaced by germ theory.

Miasma theory meant that physicians associated bad smells with disease. But they also had the evidence of their eyes. Eighteenth-century physicians saw diseases spreading easily in crowded, poorly ventilated structures, from ships and jails to the homes of the poor. Ventilation made sense as a way to make people safer: blow out the bad air. It also seemed to make a difference when they used it.

So they acted. In 1756, the British Navy ordered the installation of recently invented ventilators on ships. A naval hospital required " doors and windows to be opened for the purposes of ventilation." In 1802, the British parliament passed legislation requiring factories to have enough " Windows and Openings...to insure a proper Supply of Fresh Air."

Outbreaks in the Navy

In his 1797 book on naval medicine, physician and poet Thomas Trotter drew on his extensive experience at sea. He questioned both miasma and germ theory.

However, Trotter partly agreed with miasma theory. He was convinced that many contagious diseases, including smallpox, were spread by " the exhalations of the sick."

We now know that smallpox was spread via respiratory droplets or fine-particle aerosol. Trotter was basically right about the pathway for smallpox transmission - and a few other diseases - even though he was very wrong about how.

Eighteenth-century physicians had successes with the partial information they had. Trotter explains how they ended an outbreak of a "malignant fever" on a navy ship in 1791. They quarantined the sick, fumigated the vessel and " the ventilators worked unremittingly day and night."

Ventilation spreads

These ideas spread widely beyond medical circles through literature and kept spreading after germ theory. Writers paid a lot of attention to "exhalations." In his 1744 poem on health, John Armstrong wrote, " It is not air / That from a thousand lungs reeks back to thine." Dozens of poets repeated phrases such as "infectious breath," from Thomas Carew to Thomas Godfrey and more.

Like eighteenth-century doctors, nineteenth-century writers promoted ventilation and fresh air. In fiction, Jane Austen had her characters " breathing fresh air," while Lady Morgan complained about " thickly populated and ill ventilated " streets helping to spread disease.

Some famous poets wrote about air so much that American literary critic M.H. Abrams remarked, " That the poetry of Coleridge, Wordsworth, Shelley, [and] Byron should be so thoroughly ventilated is itself noteworthy."

Ventilation comes back

By the 1840s, the public health debate was turning to cleaner water, as germ theory began to take hold. But advances in germ theory couldn't erase the benefits of breathing fresh air from the public consciousness. Around 1850, journalist Henry Mayhew interviewed one Londoner who said the following about the city's cheap housing:

"Nothing can be worse to the health than these places, without ventilation, cleanliness, or decency, and with forty people's breaths perhaps mingling together in one foul choking steam of stench."

In 1859, Florence Nightingale helped revive ventilation in healthcare. In her book Notes on Nursing, she emphasized, " The air within as pure as the air without."

Fresh air was seen as critical during the 1918-1920 influenza pandemic as well. People were encouraged to keep windows open and move events outdoors, including court proceedings.

Now, another pandemic has got us talking about the importance of fresh air. The difference is this time we have better tools to measure and improve indoor air quality, and a much better understanding of why fresh air is good for us.

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Fresh air has long been seen as important for our health, even if we haven't always understood why

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Eighteenth-century writers worried about "infectious air," so they opened windows and built ventilation systems to bring fresh air indoors.