Primary Air Pollutants     There are two basic types of air pollutants: primary air pollutants and secondary air pollutants. Primary air pollutants enter the atmosphere directly. Secondary air pollutants form in the atmosphere from chemical reactions involving other pollutants. Some primary air pollutants have natural sources. Volcanic ash is an example. Dust is also a primary pollutant with natural sources, but humans also put dust into the air with activities such as plowing fields and building roads. Most other primary pollutants are the result of human activities alone. The majority of... Show more

Primary Air Pollutants    
There are two basic types of air pollutants: primary air pollutants and secondary air pollutants. Primary air pollutants enter the atmosphere directly. Secondary air pollutants form in the atmosphere from chemical reactions involving other pollutants. Some primary air pollutants have natural sources. Volcanic ash is an example. Dust is also a primary pollutant with natural sources, but humans also put dust into the air with activities such as plowing fields and building roads. Most other primary pollutants are the result of human activities alone. The majority of them enter the air directly from vehicles exhaust systems and smokestacks.

These primary pollutants include carbon, nitrogen, and sulfur oxides; particulates; lead; and volatile organic compounds.    
- Carbon oxides include carbon monoxide and carbon dioxide. Both are colorless, odorless gases. Carbon monoxide is toxic to both plants and animals. Both carbon monoxide and carbon dioxide are greenhouse gases.    
- Nitrogen oxides are produced when nitrogen and oxygen in the atmosphere come together at high temperatures.    
This occurs in hot exhaust gases from vehicles, power plants, and factories. Nitrogen oxides are greenhouse gases and also contribute to the formation of acid rain and ozone.    
- Sulfur oxides include sulfur dioxide and sulfur trioxide. These compounds enter the air when coal is burned.    
Sulfur oxides contribute to the formation of acid rain.    
- Particulates are solid particles, such as ash, dust, and fecal matter. Other particulates form from the combustion of fossil fuels. Particulates can produce smog and contribute to health problems such as asthma and heart disease.    
- Lead is a heavy metal that was once widely used in automobile fuels, paints, and pipes. It is now banned for these uses. Lead can cause brain damage and blood poisoning.    
- Volatile organic compounds (VOCs) are mostly hydrocarbons. The major VOC is methane, which occurs naturally but is increasing because of human activities, such as livestock raising. Methane is a greenhouse gas. 

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