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Air Trends

Air Emissions Summary Through 2005

Accelerating Progress

The Clean Air Interstate Rule (CAIR) addresses power plant emissions in 29 eastern states plus the District of Columbia . When fully implemented, CAIR will reduce SO2 emissions in these states by over 70 percent and NOx emissions by over 60 percent from 2003 levels.

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 2005, gross domestic product increased 195 percent, vehicle miles traveled increased 178 percent, energy consumption increased 48 percent, and U.S. population grew by 42 percent. During the same time period, total emissions of the six principal air pollutants dropped by 53 percent.

From 1990 to 2002, air toxics emissions declined by 42%. These reductions are the result of implementing stationary and mobile source regulations. Seventy-five percent of air toxics emitted in 2002 are included below as volatile organic compound and particulate matter emissions.

Comparison of Growth Areas and Emissions, showing that from 1970 to 2005, Gross Domestic Product has increased by 195%, vehicle miles traveled has increased by 178%, energy consumption has increased by 48%, and population has increased by 42%, while aggregate emissions of the six principal pollutants has decreased by 53%.

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 oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. PM can be directly emitted, or it can be formed when emissions of NOx, sulfur oxides (SOx), ammonia, organic compounds, and other gases react in the atmosphere. Emission estimates are based on many factors, including actual measurements, levels of industrial activity, fuel consumption, vehicle miles traveled, and other estimates of activities that cause pollution.

Emissions of air pollutants continue to play an important role in a number of air quality issues. About 141 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 programs that when fully implemented will achieve significant reductions in air emissions. The associated air quality benefits will 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 1970, 1975, 1980, 1985, 1990, 1995, 2000, and 2005. As indicated in the table, the 2005 emissions data are preliminary.

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

  Millions of Tons Per Year
  1970 1975 1980 19851 1990 1995 20001 20052
Carbon Monoxide (CO) 197.3 184.0 177.8 169.6 143.6 120.0 102.4 89
Nitrogen Oxides (NOx)3 26.9 26.4 27.1 25.8 25.2 24.7 22.3 19
Particulate Matter (PM)4








Sulfur Dioxide (SO2) 31.2 28.0 25.9 23.3 23.1 18.6 16.3 15
Volatile Organic
  Compounds (VOC)
33.7 30.2 30.1 26.9 23.1 21.6 16.9 16
Lead6 0.221 0.16 0.074 0.022 0.005 0.004 0.003 0.003
Totals7 301.5 275.8 267.2 249.2 218.2 188.0 160.2 141


  1. In 1985 and 1996 EPA refined its methods for estimating emissions. Between 1970 and 1975, EPA revised its methods for estimating particulate matter emissions.
  2. The estimates for 2005 are preliminary.
  3. NOx estimates prior to 1990 include emissions from fires. Fires would represent a small percentage of the NOx emissions.
  4. 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.
  5. EPA has not estimated PM2.5 emissions prior to 1990.
  6. The 1999 estimate for lead is used to represent 2000 and 2005 because lead estimates do not exist for these years.
  7. PM2.5 emissions are not added when calculating the total because they are included in the PM10 estimate.


To get detailed information about emissions estimates displayed above, please visit EPA's Clearinghouse for Inventories and Emissions Factors (CHIEF) Web site

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