National Analysis
Air quality in the United States improved significantly during 2002-2004, with a substantial drop in unhealthful days and fewer counties receiving failing grades than ever reported in the American Lung Association State of the Air updates. This progress occurred even though more counties were monitored for ozone and particle pollution. The most dramatic drop came in the number of days with unhealthful levels of ozone pollution. Days of unhealthful levels of particle pollution also dropped from last year’s report, but fewer particle pollution monitors were fully operating during this period.
The key factor for the remarkable decline in ozone was the final installation of controls on nitrogen oxide emissions from eastern electric utilities in 11 states in 2004.1 Beginning in 1998, the U.S. Environmental Protection Agency required most eastern states to substantially reduce emissions of nitrogen oxide (NOX), a key ingredient in ozone formation.2 During 2002-2004, 19 states implemented the required cuts in NOX emissions, largely by requiring reductions from coal-fired power plants. EPA estimates that with these controls in place, ozone levels dropped five percent per year between 2002 and 2004. In the five years before these controls were required (between 1997 and 2002), ozone levels declined only an average of one percent each year in all but two eastern states.3
Weather certainly played a part in ozone levels in several regions. Although 2002 featured a hot, dry summer that escalated ozone levels in the eastern states, the summers of 2003 and 2004 saw much cooler temperatures in those same states. Other reductions came from controls on cars, trucks and industrial processes.4
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| Reductions in nitrogen oxide emissions led to significant reductions in ozone levels, as shown here between 2002 and 2004,when most of the required controls were placed on power plants. Source: U.S. Environmental Protection Agency. EvaluatingOzone Control Programs in the Eastern United States: Focus on the NOX Budget Trading Program, 2004. August 2005. |
As a reason for the decline in particle pollution, EPA cites the Acid Rain Program for reductions in the eastern states and programs targeting direct emissions of particles in the west. Congress created the Acid Rain Program in the 1990 amendments to the Clean Air Act. The program is aimed at reducing harm over 20 years to the environment and to visibility caused by acids formed in the air from sulfur dioxide and nitrogen oxide emitted by electric utilities.5 EPA credits lower emissions to programs in the western states that paved unpaved roads, switched to natural gas from fuels like coal and wood, and improved agricultural soil management practices as tools in controlling directly emitted particles.6
Despite these improvements, much clearly remained to be done in the fight against air pollution. EPA took initial, critical steps in 2004 by formally telling the states which counties had unhealthful levels of ozone and particle pollution in response to legal action brought by the American Lung Association. In April 2004, EPA officially designated parts or all of 474 counties as “nonattainment” for the national ozone standards, which means they either have ozone levels higher than the standards allow or they contribute to pollution in a nearby county. In December, EPA followed up by designating all or part of 224 counties as nonattainment for the national particle pollution (PM2.5) standards.
The following analyses describe changes in ozone and particle pollution levels monitored in 2002, 2003 and 2004, compared to 2001-2003, the period covered by the last report, American Lung Association State of the Air 2005. This analysis covers the most current quality assured data available nationwide at press time. While some states have data from 2005 that have been quality assured, all states are not required to complete the data for 2005 until July 1, 2006.
