Since 1990, nationwide air quality has improved significantly for the six common air pollutants: ground-level ozone; particle pollution; lead; nitrogen dioxide; carbon monoxide; and sulfur dioxide, according to the US Environmental Protection Agency (EPA) report “Our Nation’s Air - Status and Trends through 2008”. Nationally, air pollution was lower in 2008 than in 1990 for:
- 8-hour ozone, by 14%
- annual PM2.5 (since 2000), by 19%
- PM10, by 31%
- Lead, by 78%
- NO2, by 35%
- 8-hour CO, by 68%
- annual SO2, by 59%
Toxic air pollutants such as benzene, 1,3-butadiene, styrene, xylenes, and toluene decreased by 5% or more per year between 2000 and 2005 at more than half of ambient monitoring sites. Other key contributors to cancer risk, such as carbon tetrachloride, tetrachloroethylene, and 1,4-dichlorobenzene, declined at most sites. Total emissions of toxic air pollutants have decreased by approximately 40% between 1990 and 2008.
Despite this progress, about 127 million Americans live in counties violating at least one of the national air quality standards. The agency has taken recent actions further to tighten air quality standards.
EPA expects air quality to continue to improve as recent regulations are fully implemented and states work to meet current and recently revised national air quality standards. Key regulations include the Locomotive Engines and Marine Compression-Ignition Engines Rule; the Tier II Vehicle and Gasoline Sulfur Rule; the Heavy-Duty Highway Diesel Rule; the Clean Air Non-Road Diesel Rule; and the Mobile Source Air Toxics Rule.