Study Notes on Air Pollution and Criteria Air Pollutants

Definition of Air Pollution: The presence of harmful substances (pollutants) in the air, which can be specific molecules or particles.
Clean Air Act (1970): A significant piece of legislation that identifies six criteria air pollutants that the Environmental Protection Agency (EPA) is required to set acceptable limits for, monitor, and enforce.

SO₂ (Sulfur Dioxide)
- Source: Primarily produced from coal combustion in electricity generation.
- Effects: Respiratory irritant, can cause acid precipitation.
NOx (Nitrogen Oxides)
- Components: Includes both nitrogen monoxide (NO) and nitrogen dioxide (NO₂).
- Source: Emitted from the combustion of fossil fuels (especially gas).
- Effects: Contributes to smog and respiratory issues. Facilitates the formation of ozone (O₃) through photochemical reactions.
CO (Carbon Monoxide)
- Source: Produced by the incomplete combustion of fossil fuels.
- Effects: Lethal to humans as it interferes with the body's ability to transport oxygen.
PM (Particulate Matter)
- Source: Emitted from various sources, including fossil fuel and biomass combustion.
- Effects: Respiratory irritant, contributes to smog.
Ozone (O₃)
- Type: Tropospheric ozone.
- Formation: Results from the photochemical oxidation of NO₂ under sunlight.
- Effects: Causes respiratory irritation and plant damage.
Pb (Lead)
- Source: Emitted from metal plants, waste incineration.
- Effects: Neurotoxicant that can damage the nervous systems of humans.

CO₂ (Carbon Dioxide)
- Classification: Not classified as a criteria pollutant in the Clean Air Act, although the Supreme Court ruling in 2007 allowed the regulation of greenhouse gases.
- Characteristics:
- Does not directly lower air quality from a human health standpoint.
- Not toxic when inhaled; does not damage lungs or eyes.
- Does not cause decreased visibility.
- Environmental Impact: While CO₂ is not a direct air pollutant, it is a greenhouse gas that contributes to global warming and can have indirect human health consequences.
Importance for AP Environmental Science (APES): CO₂ has not typically been included in discussions about air pollutants in APES curricula. Focus should remain on criteria pollutants like SO₂, NOx, and O₃.

Significance: Coal combustion is responsible for releasing more air pollutants than other fossil fuel sources, contributing to about 35% of global electricity.
Emissions: Releases a variety of pollutants including CO₂, CO, NOx, toxic metals (mercury, arsenic, lead), and particulate matter (PM).

Health Impacts: Acts as a respiratory irritant, potentially worsening asthma and leading to chronic bronchitis. Contributes to the formation of sulfur aerosols which block sunlight.
Chemical Reactions: Combines with water (H₂O) and oxygen (O₂) in the atmosphere to form sulfuric acid, leading to acid precipitation.

Sources: Released by combustion of fossil fuels, biomass, and other organic materials.
Chemical Formations: NO forms when nitrogen (N₂) combines with oxygen (O₂) during combustion and can further react to become NO₂.
Environmental Impact: Contributes to the formation of tropospheric ozone (O₃), which leads to respiratory irritations and environmental damage.

Lead Regulation: Historically, lead was a common additive in gasoline, contributing to air pollution before the EPA phased it out starting in 1924.
Catalytic Converters: Vehicles manufactured after 1974 must include catalytic converters to minimize emissions of NOx, CO, and hydrocarbons, as lead can damage these converters.

Primary Pollutants:
- Definition: Pollutants that are emitted directly from sources such as vehicles, power plants, factories, or natural occurrences (e.g., volcanoes, forest fires).
- Examples: NOx, CO, CO₂, VOCs, SO₂, PM.
Secondary Pollutants:
- Definition: Result from the transformation of primary pollutants in the presence of sunlight, water, and oxygen.
- Examples: Ozone (O₃), sulfuric acid (H₂SO₄), and nitrate (NO₃⁻).