Sulfur oxides (SOx), especially sulfur dioxide, which is a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Since coal and oil often contain sulfur compounds, their combustion generates sulfur dioxide. 

Carbon monoxide is colorless, odorless, non-irritating, but very poisonous. It is a product of the incomplete combustion of fuels such as natural gas, coal or wood. Vehicles are one of the main sources of carbon monoxide. Carbon dioxide (CO2) is a greenhouse gas emitted by combustion. Methane: it is an efficient greenhouse gas that contributes to a greater warming of the Earth. Scents such as garbage, sewage, and industrial processes. Radioactive contaminants produced by nuclear explosions, explosives, and natural processes, such as radioactive disintegration of radon.