7.1 Introduction to Air Pollution

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Vocabulary

• 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) is a colorless and odorless gas that is produced by the incomplete burning of fossil fuels, such as gasoline and natural gas. It is a primary pollutant that can have serious health effects, including headaches, dizziness, and nausea. In severe cases, it can lead to coma and death.
• Nitric oxide (NO) is a gas that is produced by the burning of fossil fuels and the reaction of nitrogen and oxygen in the atmosphere. It is a primary pollutant that can contribute to the formation of ground-level ozone and particulate matter.
• Nitrogen dioxide (NO2) is a gas that is produced by the burning of fossil fuels and the reaction of nitrogen and oxygen in the atmosphere. It is a primary pollutant that can contribute to the formation of ground-level ozone and particulate matter. It can also have adverse effects on human health, including respiratory problems.
• Sulfur dioxide (SO2) is a gas that is produced by the burning of fossil fuels that contain sulfur, such as coal and oil. It is a primary pollutant that can contribute to the formation of particulate matter and acid rain. It can also have adverse effects on human health, including respiratory problems.
• Ammonia (NH3) is a gas that is produced by the breakdown of organic matter and the use of fertilizers. It is a primary pollutant that can contribute to the formation of particulate matter and the degradation of air quality. It can also have adverse effects on human health, including respiratory problems.
• Volatile organic compounds (VOCs) are organic compounds that evaporate easily at room temperature and can contribute to air pollution. They are emitted by a variety of sources, including industrial processes, paints, and cleaning products. VOCs are a primary pollutant that can contribute to the formation of ground-level ozone and particulate matter. They can also have adverse effects on human health, including respiratory problems and cancer.
• Particulate matter (PM) is a mixture of solid particles and liquid droplets that are suspended in the air. It is a primary pollutant that can have adverse effects on human health, including respiratory problems and cardiovascular disease. PM can be emitted by a variety of sources, including power plants, industrial processes, and transportation. It is classified by size, with PM10 being particles that are 10 micrometers or smaller in diameter, and PM2.5 being particles that are 2.5 micrometers or smaller in diameter. PM2.5 is particularly harmful because it is small enough to be inhaled and can penetrate deep into the respiratory system.

Secondary Pollutants

• Sulfur trioxide (SO3) is a gas that is produced by the burning of fossil fuels that contain sulfur, such as coal and oil. It can react with water vapor in the atmosphere to form sulfuric acid, which is a secondary pollutant.
• Sulfuric acid (H2SO4) is a strong acid that is produced by the reaction of sulfur trioxide with water vapor in the atmosphere. It is a secondary pollutant that can contribute to the formation of particulate matter and acid rain.
• Nitric acid (HNO3) is a strong acid that is produced by the reaction of nitrogen dioxide with water vapor in the atmosphere. It is a secondary pollutant that can contribute to the formation of particulate matter and acid rain.
• Ozone (O3) is a gas that is produced by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight. It is a secondary pollutant that can have adverse effects on human health, including respiratory problems.
• Ammonium (NH4) is a compound that is produced by the reaction of ammonia with acids in the atmosphere. It is a secondary pollutant that can contribute to the formation of particulate matter.
• Particulate matter (PM) is described above.

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