EPA presents most recent emission trends for the U.S.
Emissions causing poor air quality across the U.S. have declined since 1970 while we have experienced significant economic growth.

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"The Ozone Report: Measuring Progress through 2003", lays the groundwork for the planning and analysis needed to track progress toward attaining the nation's more protective 8-hour ozone standard and reporting the results to the public.

Ozone levels across the nation were down substantially in 2003. The improved air quality resulted from favorable weather conditions and continuing reductions in emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) – the pollutants that combine in the summer heat to form ozone.

Under the Clean Air Act, EPA establishes air quality standards to protect public health and the environment. EPA has set national air quality standards for the six principal air pollutants. These include: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NOx), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2).

Each year EPA looks at the levels of these pollutants in the air and the amounts of emissions from various sources to see how both have changed over time and to summarize the current status of air quality. EPA posts the results of our analyses to this website.

EPA tracks air pollution in two ways: air quality and emissions.

• Trends in air quality are based on actual measurements of pollutant concentrations in the ambient (outside) air at monitoring sites across the country. Monitoring stations are operated by state, tribal, and local government agencies as well as some federal agencies, including EPA. Trends are derived from direct measurements from these monitoring stations on a yearly basis.
• EPA estimates nationwide emissions of the six principal air pollutants and the 188 toxic air pollutants regulated under the Clean Air Act. These estimates are based on many factors, including actual measurements, levels of industrial activity, fuel consumption, vehicles miles traveled, and other estimates of activities that cause pollution.