Pollutants and their Effects
Table of Contents
- Working Together for Cleaner Air
- Pollutants and their Effects
- The Acid Rain Challenge
- Preserving Air Quality for Today and Tomorrow
- Key Commitments of the Ozone Annex
- Progress on Ground-Level Ozone
- Other Air Quality Programs
- Cooperation on Emission Inventories, Trends, and Mapping
- Research Efforts on Effects of Air Pollution
- A History of Cooperation
- For More Information
Acid deposition, more commonly known as acid rain, occurs when emissions of SO2 and NOx from power plants, vehicles, and other sources react in the atmosphere (with water, oxygen, and oxidants) to form various acidic compounds. These acidic compounds then fall to earth in either a wet form (rain, snow, or fog) or a dry form (gases and particles) and can harm aquatic and terrestrial ecosystems (particularly forests); affect human health; impair visibility; and damage automotive finishes, buildings, bridges, monuments, and statues.
Ground-level ozone is a gas that forms when emissions of NOx and VOCs react with other chemicals in the air in the presence of strong sunlight. NOx and VOCs are emitted by combustion sources (such as vehicles and power plants). VOCs are also given off by solvents, cleaners, and paints. Ground-level ozone can cause or exacerbate respiratory illnesses, and is especially harmful to young children, the elderly, and those suffering from chronic asthma and/or bronchitis. Ground-level ozone can affect leaves and roots of plants, especially trees. This can make them more susceptible to attack from insects and diseases and can reduce their ability to withstand droughts, windstorms, and manmade stresses such as acid rain.
PM includes both solid particles and liquid droplets found in the air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. PM comes in a range of sizes and is associated with numerous health effects. Particles less than 10 micrometers in diameter (PM10)—especially those less than 2.5 micrometers in diameter (PM2.5)—pose the greatest health risk because they can be inhaled and accumulate in the respiratory system. Sulfates (SO4) and nitrates (NO3) formed from SO2 and NOx are significant components of PM2.5. PM is also a major contributor to regional haze, which reduces visibility.