Environmental Protection Agency

The Clean Air Act directs EPA to establish air quality standards to protect public health and the environment. EPA sets national air quality standards for six principal air pollutants (also called the criteria pollutants): nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), particulate matter (PM), carbon monoxide (CO), and lead (Pb).

Looking at Growth and Emissions
Each year EPA looks at emissions that impact the ambient concentrations of these pollutants. These annual emissions estimates are used as one indicator of the effectiveness of our programs. The graph below shows that between 1970 and 2003, gross domestic product increased 176 percent, vehicle miles traveled increased 155 percent, energy consumption increased 45 percent, and U.S. population grew by 39 percent. During the same time period, total emissions of the six principal air pollutants dropped by 51 percent.

From 1990 to 1999, air toxics emissions have declined by 30%. These reductions are the result of implementing stationary and mobile source regulations. Eighty-four percent of air toxics are included below as volatile organic compound and particulate matter emissions.

Chart showing comparison of growth areas and emissions from 1970 to 2003

Estimating Emissions
EPA estimates nationwide emissions of ambient air pollutants and the pollutants that form them (their precursors). Four of the principal pollutants (CO, Pb, NO2 , and SO2) are emitted directly from a variety of sources. Ozone is generally not directly emitted, but is formed when NO2 volatile organic compounds (VOCs) react in the presence of sunlight. PM can be directly emitted, or it can be formed when emissions of nitrogen oxides (NO2), sulfur oxides (SO2), ammonia, organic compounds, and other gases react in the atmosphere.

Emissions of air pollutants continue to play an important role in a number of air quality issues. About 160 million tons of pollution are emitted into the atmosphere each year in the United States. These emissions contribute to the formation of ozone and particles, the deposition of acids, and visibility impairment.

In recent years, EPA has acted to dramatically improve America’s air quality by providing national tools, that when fully implemented will achieve significant reductions in air emissions. The associated air quality benefits lead to improved health, longevity and quality of life for all Americans.

The table below examines changes in national estimates of emissions for the major air pollutants or, where appropriate, precursor pollutants that form them. The table includes emissions data for 1990, 1995, 2000 and 2003. As indicated in the table, the 2003 emissions data are preliminary. Note that EPA would normally release nationwide emissions estimates as part of the Annual Report on National Air Quality and Emissions Trends. This year, EPA issued a special version for ozone air quality trends in May. It expects to issue trends for particle pollution later this year.

National Air Pollutant Emissions Estimates
(fires and dust excluded)
For Major Pollutants

Table showing national air pollutant emissions estimates for major pollutants (excluding fires and dust)

Notes:

In 1985 and 1996 EPA refined its methods for estimating emissions. Between 1970 and 1975, EPA revised its methods for estimating particulate matter emissions.
The estimates for 2003 are preliminary.
NOx estimates prior to 1990 include emissions from fires. Fires would represent a small percentage of the NOx emissions.
PM estimates do not include condensable PM, or the majority of PM2.5 that is formed in the atmosphere from 'precursor' gases such as SO2 and NOx.
EPA has not estimated PM2.5 emissions prior to 1990.
The 1999 estimate for lead is used to represent 2000 and 2003 because lead estimates do not exist for these years.
PM2.5 emissions are not added when calculating the total because they are included in the PM10 estimate.

You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

More details on the preliminary 2003 emissions totals are available, including:

		Related Links \| Acronyms \| Hardcopies


		EPA Home \| Privacy and Security Notice \| Contact Us

Air Emissions Trends - Continued Progress Through 2003