Criteria Pollutants: The U.S. Clean Air Act identifies six major air pollutants:
Sulfur Dioxide (SO2): Formed from burning fossil fuels (coal, oil).
Nitrogen Oxides (NOx): Formed at high temperatures in combustion processes, contributes to smog and acid rain.
Carbon Monoxide (CO): Produced by incomplete combustion, a toxic gas that interferes with oxygen transport in blood.
Ozone (O3): Beneficial in the stratosphere (blocks UV), harmful at ground level (contributes to smog).
Particulate Matter (PM10, PM2.5): Includes solid particles and liquid droplets. Health risks increase with smaller particles.
Lead (Pb): Neurotoxic metal, major source from burning of fossil fuels, particularly coal.
Sources of Air Pollution
Natural Sources: Volcanoes, vegetation release VOCs, and sea spray.
Anthropogenic Sources: Primary pollutants (directly emitted) vs. secondary pollutants (formed by reactions in the atmosphere).
Criteria Pollutant Sources:
SO2: 2 million tons from stationary combustion
NOx: 9 million tons from stationary combustion and vehicles
CO: 64 million tons primarily from transportation
VOCs: 17 million tons from various sources (both natural and anthropogenic)
Particulate Materials: 17 million tons from various activities.
Atmospheric Processes
Troposphere: The lowest layer of the atmosphere where weather occurs. Air temperature decreases with altitude.
Tropopause: The boundary between the troposphere and the stratosphere, restricting vertical mixing.
Industrial & Photochemical Smog
Industrial Smog: Results from the burning of coal, primarily composed of SO2 and PM.
Photochemical Smog: Initiated by sunlight, involves VOCs and NOx leading to ozone formation. Secondary pollutants infused, contributing to urban air quality issues.
Acid Rain
Definition: Rain (or precipitation) that has a pH lower than 5.6. Formed from sulfuric acid (H2SO4) and nitric acid (HNO3), primarily due to pollution.
Effects: Can damage forests, wildlife, and structures/materials (e.g., limestone, marble).
Control of Air Pollution
Legislation: The Clean Air Act regulates pollutants.
Pollution Control Methods:
Electrostatic Precipitation: Uses electrical charges to remove particles from exhaust.
Bag Filtration: Captures particulates using fabric bags similar to vacuum cleaners.
Trends in U.S. Air Quality: Air quality has improved in recent decades, with reductions in emission levels of criteria pollutants.
Effects of Air Pollution
Health Impacts: WHO estimates linked millions of premature deaths to air pollution, particularly from PM2.5 exposure.
Risks include respiratory diseases, heart attacks, and complications in fetal development.
Indoor Air Pollution
Often higher concentrations of toxic pollutants compared to outdoors due to materials in use at home (e.g., formaldehyde, benzene).
Common Indoor Pollutants: Asbestos, CO, lead, nitrogen dioxide, VOCs, etc.