The leading cause of air pollution is the burning of fossil fuels, but other pollutants, such as pollen, smoke from fires and the gases given off from organisms while they are decaying, also contribute. Air pollution is caused by both human activities and naturally occurring events.
The burning of fossil fuels contributes to the largest amount of air pollution mostly due to the fact that many human activities are directly related to the use of gasoline and other fuels in order to keep items such as engines and furnaces running. The largest source of air pollution due to fossil fuels being burned is vehicles. Due to their large number and the length of time they are run, carbon monoxide, the gas given off by trucks and cars, is constantly released into the air.
Another form of air pollutant produced by vehicles is carbon dioxide, which is not considered as deadly as carbon monoxide, which causes adverse health effects. It is closely related to the greenhouse effect, which is considered to be the cause of the warming of the earth.
Outside of burning fossil fuels, other pollutants are released into the air due to the burning of certain materials. Particulate matter is the direct result of burning items such as wood and plants, which happens both from human activity and natural fires.