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AP Enviro



Unit 7

7.1 Introduction to Air Pollution

2 min readmay 29, 2020

Joshua Nielsen


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  • Primary Pollutants

  • Secondary Pollutants

  • NOx

  • SOx

  • COx

  • Clean Air Act

  • Hydrocarbons

  • Particulates

Coal and Fossil Fuels

The burning of coal and fossil fuels releases many gasses and particles. Coal combustion will release carbon dioxide, sulfur dioxide, metals such as mercury and lead, and particulates. Fossil fuel combustion generates carbon monoxide, nitrogen oxides, sulfur dioxides, hydrocarbons, and particulates

As there are various forms of some of these gasses, they are often referred to as the SOx (sulfur oxides), NOx (nitrogen oxides), and carbon oxides. The small ‘x’ denotes the number of oxygens in the chemical formula.

There are other sources of air pollutants such as factories, volcanoes, and campfires. They produce most of the same gasses and particulates as coal and fossil fuels.

Primary and Secondary Pollutants

Many of the gasses undergo changes and are therefore referred to as either primary or secondary pollutants. Primary pollutants are those that are emitted directly from a source. Primary sources include internal combustion vehicles, wildfires, factories, coal-burning power plants, agriculture, and volcanoes.

Secondary pollutants have undergone a change from a primary pollutant. These changes are often due to the gasses interacting with water vapor and/or sunlight.  Smog and acid precipitation are both examples of secondary pollutants.

Primary Pollutants

  • Carbon monoxide (CO)

  • Nitric oxide (NO)

  • Nitrogen dioxide (NO2)

  • Sulfur dioxide (SO2)

  • Ammonia (NH3)

  • Volatile organic compounds (VOCs)

  • Particulate matter (PM)

Secondary Pollutants

  • Sulfur trioxide (SO3)

  • Sulfuric acid (H2SO4)

  • Nitric acid (HNO3)

  • Ozone (O3)

  • Ammonium (NH4)

  • Particulate matter (PM)

Air Quality

Air quality is affected by the amounts of various gasses and particulates found in the atmosphere. These pollutants may cause brown or grey smog, ozone warnings, or acid precipitation.

The Clean Air Act was passed in 1963 in order to control what is released into the air. It has since gone through many changes. It is largely responsible for the reduction of lead in the atmosphere and currently helps to reduce acid rain and protect the ozone layer. 

Watch: AP Environmental Science - Air Pollution


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