2.3 Atmospheric chemistry and air pollution

Air pollution is a complex issue with far-reaching effects on health and the environment. From smog to acid rain, various pollutants form through chemical reactions in the atmosphere, causing respiratory problems, ecosystem damage, and infrastructure corrosion.

Strategies to combat air pollution include emission control technologies, clean energy transitions, and improved transportation systems. These efforts, combined with effective policies and regulations, aim to reduce pollutants at their source and create cleaner, healthier air for everyone.

Atmospheric Chemistry and Air Pollution

Formation and effects of air pollutants

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• Smog formation occurs through photochemical and industrial processes
  • Photochemical smog produced in sunlight with nitrogen oxides (NOx) and volatile organic compounds (VOCs) creating ground-level ozone and oxidants
  • Industrial smog results from burning coal and fossil fuels containing sulfur dioxide (SO2), NOx, and particulate matter (soot, ash)
• Acid rain forms when SO2 and NOx react with atmospheric water vapor
  • Creates sulfuric acid (H2SO4) and nitric acid (HNO3) that fall as precipitation (rain, snow)
• Smog effects include respiratory issues (asthma, lung irritation), reduced visibility, and damage to plants and crops (leaf damage, stunted growth)
• Acid rain effects include acidification of lakes and streams harming aquatic life (fish, amphibians), damage to forests and vegetation (leaf loss, stunted growth), and corrosion of buildings and infrastructure (limestone, marble)

Role of photochemical reactions in ozone

• Photochemical reactions involve molecules absorbing sunlight leading to chemical changes
• Tropospheric ozone formation:
  1. Nitrogen dioxide (NO2) absorbs sunlight and dissociates into nitric oxide (NO) and atomic oxygen (O): $NO2 + sunlight → NO + O$
  2. Atomic oxygen reacts with molecular oxygen (O2) to form ozone (O3): $O + O2 + M → O3 + M$, where M is a third molecule absorbing excess energy
  3. Ozone can react with NO to regenerate NO2: $O3 + NO → NO2 + O2$
• Ozone formation influenced by presence of NOx and VOCs, sunlight intensity, temperature, and atmospheric stability (inversion layers)

Sources and impacts of particulate matter

• Primary particulate matter sources include direct emissions from combustion (vehicles, power plants), dust from construction, unpaved roads, and agriculture (tilling, harvesting)
• Secondary particulate matter forms through atmospheric chemical reactions such as oxidation of SO2 and NOx
• Human health impacts include respiratory issues (asthma, bronchitis, lung cancer), cardiovascular problems (heart attacks, strokes), and premature death in people with pre-existing heart or lung diseases
• Environmental impacts include reduced visibility from haze, altered nutrient balance in ecosystems (nitrogen deposition), and climate change through direct and indirect effects on Earth's radiative balance (scattering, absorption)

Strategies for reducing air pollution

• Emission control technologies reduce pollutants at the source
  • Catalytic converters in vehicles reduce NOx and VOC emissions
  • Scrubbers in industrial smokestacks remove SO2 and particulate matter
• Clean energy transition shifts from fossil fuels to renewable sources (solar, wind) and promotes energy efficiency and conservation (insulation, LED lighting)
• Transportation improvements encourage public transit, carpooling, active transportation (walking, cycling), and stricter vehicle fuel efficiency standards
• Policy and regulations set and enforce air quality standards, implement cap-and-trade programs or carbon taxes to limit emissions, and promote urban planning and land use strategies that reduce air pollution (green spaces, compact development)