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Air Trends

Fact Sheet - 1996 Air Trends Report


Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.


EPA Document Number 454/R-97-013

1-23-98

Highlights

  • Since 1970, air quality has continued to improve for six major air pollutants known as "criteria" pollutants. They include carbon monoxide, lead, nitrogen dioxide, ground-level ozone, particulate matter, and sulfur dioxide. Emissions of all of these pollutants except nitrogen oxides have decreased significantly since 1970. Between 1970 and 1996 emissions of NOx have increased 8 percent. Emissions of NOx contribute to the formation of ozone. In October, 1997 EPA proposed a rule that will significantly reduce emissions of NOx in 22 eastern states, and, in turn, reduce the regional transport of ozone.
  • The improvements in air quality and economic prosperity that have occurred since EPA initiated air pollution control programs in the early 1970s illustrate that economic growth and environmental protection can go hand-in-hand. Since 1970, national total emissions of the six criteria pollutants declined 32 percent, while U.S. population increased 29 percent, gross domestic product increased 104 percent, and vehicle miles traveled increased 121 percent.
  • Nationally, the 1996 air quality levels are the best on record for all six criteria pollutants. In fact, all the years throughout the 1990s have had better air quality than any of the years in the 1980s, showing a steady trend of improvement.
  • Despite continued improvements in air quality, approximately 46 million people lived in counties that did not meet the air quality standards for at least one of the six criteria pollutants in 1996.

Background

  • For the past 24 years, EPA has examined the air pollution trends of the six criteria pollutants. The 1996 National Air Quality and Emissions Trends Report discusses the nation's progress in cleaning up these pollutants during the 10-year period between 1987 and 1996.
  • In the report, EPA tracks trends in concentrations and emissions of these six pollutants. Air quality information is based on actual measurements of pollutant concentrations in the air from nearly 5000 monitoring sites located throughout the nation. Air pollutant emission trends are based on engineering estimates of the total tonnage these pollutants released to the air annually. However, starting in 1994, under the Acid Rain Program, EPA began tracking measured emission values of sulfur dioxide and nitrogen oxides based on actual emissions data from continuous emission monitors for the electric utility industry.
  • Generally there are similarities between air quality trends and emission trends for any given pollutant. However, in some cases, there are notable differences between the percent change in ambient concentrations and the percent change in emissions. These differences can mainly be attributed to the location of air quality monitors. Most monitors are positioned in urban, population-oriented locales which are more likely to indicate reductions in emissions that occur in urban areas (such as emissions from automobiles) rather than emissions that occur in rural areas (such as emissions from power plants). Thus, trends in air quality more closely track changes in urban emissions rather than changes in total national emissions.
  • In July 1997, EPA revised the ozone and particulate matter standards following a lengthy scientific review process. Prior to this time, the PM standard applied to particles whose aerodynamic size is less than or equal to 10 micrometers, or PM10. The NAAQS revision strengthened protection against particles in the smaller part of that range by adding an indicator for PM2.5 (those whose aerodynamic size is less than or equal to 2.5 micrometers). The combination of the PM10 and PM2.5 indicators will provide protection against a wide array of particles.

Health Effects and Trends in Air Pollutants

Carbon Monoxide (CO)

  • Carbon monoxide enters the bloodstream through the lungs and reduces oxygen delivery to the body's organs and tissues. The health threat from CO is most serious for those who suffer from cardiovascular disease. At higher levels of exposure, healthy individuals are also affected. Visual impairment, reduced work capacity, reduced manual dexterity, poor learning ability, and difficulty in performing complex tasks are all associated with exposure to elevated CO levels. Automobiles are a large source of emissions of carbon monoxide.
  • Over the past 10 years, ambient concentrations of CO decreased 37 percent, and the estimated number of exceedances of the 8-hour standard decreased 92 percent. Also, CO emissions decreased 18 percent, and CO emissions from highway vehicles decreased 26 percent. These improvements occurred despite a 28 percent increase in vehicle miles traveled during this 10-year period. Between 1995 and 1996, ambient CO concentrations decreased 7 percent and emissions of CO decreased 1 percent.

Lead (Pb)

  • Exposure to lead occurs mainly through the inhalation of air and the ingestion of lead in food, water, soil, or dust. It accumulates in the blood, bones, and soft tissues. Because it is not readily excreted, lead can also adversely affect the kidneys, liver, nervous system, and other organs. Excessive exposure to lead may cause neurological impairments such as seizures, mental retardation, and/or behavioral disorders. At low doses, fetuses and children often suffer from central nervous system damage. Recent studies also show that lead may be a factor in high blood pressure and subsequent heart disease.
  • Historically, automobiles have been the largest source of emissions of lead. However, the widespread use of unleaded gasoline has dramatically reduced the contribution from automobiles worldwide. Industrial processes (e.g., metals processing) are another significant source of lead emissions.
  • Between 1987 and 1996, ambient lead concentrations decreased 75 percent, and lead emissions decreased 50 percent. Lead emissions from highway vehicles have decreased 99 percent since 1987 as a result of the increased use of unleaded gasoline and the reduction of the lead content in leaded gasoline. Between 1995 and 1996, lead concentrations remained unchanged, total lead emissions decreased 2 percent, and lead emissions from transportation sources did not change. While lead emissions from industrial sources have dropped more than 90 percent since the late 1970s, some serious point-source lead problems remain.

Nitrogen Dioxide (NO2)

  • Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza. The effects of short-term exposure are still unclear, but continued or frequent exposure to concentrations higher than those normally found in the ambient air may cause increased incidence of acute respiratory disease in children. Nitrogen oxides are an important precursor to both ozone and acidic precipitation (acid rain) and can affect both terrestrial and aquatic ecosystems. The regional transport and deposition of nitrogenous compounds arising from emissions of NOx is a potentially significant contributor to such environmental effects as the growth of algae and subsequent unhealthy or toxic conditions for fish in the Chesapeake Bay and other estuaries. In some parts of the western United States, NOx have a significant impact on particulate matter concentrations. Automobiles and fuel combustion (e.g., electric utilities) are a significant source of emissions of nitrogen dioxide.
  • Between 1987 and 1996, ambient concentrations of NO2 decreased 10 percent, but total emissions of nitrogen oxides (NOx) increased 3 percent, due primarily to increased emissions from non-utility fuel combustion. Between 1995 and 1996, national average annual mean NO2 ambient concentrations remained unchanged, while total emissions of NOx decreased 2 percent. Emissions from highway vehicles, also a source of NOx emissions, decreased 6 percent between 1987 and 1996, while NOx emissions from utility fuel combustion decreased 3 percent.

Ozone (O3)

  • Ozone occurs naturally in the stratosphere and provides a protective layer high above the earth. At ground-level, however, it is the prime ingredient of smog. Short-term exposures (1 to 3 hours) to ambient ozone concentrations have been linked to increased hospital admissions and emergency room visits for respiratory causes. Repeated exposures to ozone can make people more susceptible to respiratory infection and lung inflammation, and can aggravate preexisting respiratory diseases such as asthma. Other health effects attributed to short-term exposures to ozone, generally while individuals are engaged in moderate or heavy exertion, include significant decreases in lung function and increased respiratory symptoms such as chest pain and cough.
  • Children active outdoors during the summer when ozone levels are at their highest are most at risk of experiencing such effects. Other at-risk groups include outdoor workers, individuals with preexisting respiratory disease such as asthma and chronic obstructive lung disease, and individuals who are unusually responsive to ozone. Recent studies have attributed these same health effects to prolonged exposures (6 to 8 hours) to relatively low ozone levels during periods of moderate exertion. In addition, long-term exposures to ozone present the possibility of irreversible changes in the lungs which could lead to premature aging of the lungs and/or chronic respiratory illnesses.
  • The regional transport of ozone is a problem, particularly in the eastern United States. Ozone is not emitted directly into the air, rather it is formed when volatile organic compounds react in the presence of sunlight. In order to address ozone pollution, EPA has traditionally focused its control strategies on reducing emissions of volatile organic compounds in individual nonattainment areas. However, EPA and the States have recognized a need for an aggressive program to reduce regional emissions of nitrogen oxides. In October, 1997 EPA proposed a rule that will significantly reduce emissions of NOx in 22 eastern states, and, in turn, reduce the regional transport of ozone. National trends in emissions of NOx and VOC underscore the importance of this new approach. Between 1970 and 1996 emissions of VOCs have decreased 38 percent whereas emissions of NOx have increased 8 percent. Further, between 1987 and 1996 emissions of VOCs have decreased 18 percent whereas emissions of NOx have increased 3 percent.
  • Between 1987 and 1996, ambient ozone concentrations decreased 15 percent, and the estimated number of exceedances of the ozone standard decreased 73 percent. Between 1995 and 1996, ambient ozone concentrations decreased 6 percent, while the estimated number of exceedances of the ozone standard decreased 37 percent. VOC emissions decreased 18 percent between 1987 and 1996 and decreased 7 percent between 1995 and 1996. NOx emissions, the other main ozone precursor, increased 3 percent between 1987 and 1996 and decreased 2 percent from 1995 to 1996.
  • On July 18, 1997, EPA revised the national ambient air quality standards for ozone and particulate matter. After a lengthy scientific review process, including extensive external scientific review, and public review and comment, EPA issued a rule that will replace the previous 1-hour ozone 0.12 parts per million (ppm) standard with a new 8-hour 0.08 ppm standard to better protect public health and the environment. Although areas that do not meet the new 8-hour standard will not be designated "nonattainment" until the year 2000, the National Air Quality and Emissions Trends Report can begin to track trends in 8-hour levels of ozone. Nationally, 8-hour levels of ozone have decreased 11 percent over the past 10 years.

Particulate Matter (PM10)

  • Scientific studies show a link between particulate matter (alone, or combined with other pollutants in the air) and a series of significant health effects. These health effects include premature death, increased hospital admissions and emergency room visits, increased respiratory symptoms and disease, decreased lung function, and alterations in lung tissue and structure and in respiratory tract defense mechanisms. Sensitive groups that appear to be at greatest risk to such effects include the elderly, individuals with cardiopulmonary disease such as asthma, and children. In addition to health problems, particulate matter is the major cause of reduced visibility in many parts of the United States. Airborne particles also can cause soiling and damage to materials. Emissions of PM10 come from a variety of sources including windblown dust and grinding operations.
  • Ambient PM10 concentrations decreased 25 percent between 1988 and 1996 and decreased 4 percent between 1995 and 1996. PM10 estimated emissions (excluding fugitive emissions and emissions from natural sources) decreased 12 percent between 1988 and 1996 and remained unchanged between 1995 and 1996.
  • On July 18, 1997 EPA revised the national ambient air quality standards for particulate matter. After a lengthy scientific review, EPA determined that the annual PM10 standard set at 50 micrograms per cubic meter (ug/m3) should not change but that the form of the PM10 24-hour standard (which remains at a level of 150 ug/m3) should be revised. Further, these studies indicated serious health risk associated with exposure to particles in the smaller part of that range. Therefore, EPA added an indicator for PM2.5 (those whose aerodynamic size is less than or equal to 2.5 micrometers). The combination of the PM10 and PM2.5 indicators will provide protection against a wide array of particles. The annual PM2.5 standard is set at 15 ug/m3 and the 24-hour PM2.5 standard set at 65 ug/m3. The secondary (welfare-based) standards were also revised by making them identical to the primary (health-based) standards. In conjunction with the Regional Haze Program, the secondary standards will protect against major PM welfare effects, such as visibility impairment, soiling, and materials damage. In July, 1997, EPA proposed a rule to address regional haze, and EPA plans to finalize this rule in July, 1998.
  • As the implementation of these revised standards begins and a national air quality monitoring network for PM2.5 is established, the National Air Quality and Emissions Trends Report will track trends in concentrations of PM2.5.

Sulfur Dioxide (SO2)

  • The major health concerns associated with exposure to high concentrations of SO2 include effects on breathing, respiratory illness, alterations in the lungs' defenses, and aggravation of existing cardiovascular disease. Major subgroups of the population that are most sensitive to SO2 include asthmatics and individuals with cardiovascular disease or chronic lung disease, as well as children and the elderly. Fuel combustion (e.g., from electric utilities) is a significant source of emissions of sulfur dioxide.
  • Between 1987 and 1996, ambient concentrations of SO2 decreased 37 percent, while emissions of SO2 decreased 14 percent. Between 1995 and 1996, nationwide average ambient SO2 concentrations remained unchanged, while SO2 emissions increased 3 percent. SO2 emissions from electric utilities decreased 20 percent between 1987 and 1996. Between 1995 and 1996, SO2 emissions from electric utilities increased 4 percent. The recent reductions in SO2 emissions from electric utilities (down 17 percent since 1993) are due, in large part, to controls implemented under EPA's Acid Rain Program. The increase in SO2 emissions that occurred between 1995 and 1996 is primarily due to increased demand for electricity.

For Further Information

  • Interested parties can download the report from the EPA's web site on the Internet at the following address: (http://www.epa.gov/airtrends/aqtrnd96/). To order copies of the report, contact Linda Ferrell of EPA's Office of Air Quality Planning and Standards at (919) 541-5558 or by electronic mail at ferrell.linda@epamail.epa .gov.
  • For questions about the report, contact David Mintz of EPA's Office of Air Quality Planning and Standards at (919) 541-5224 or by electronic mail, mintz.david@epamail.epa.gov .
  • The EPA's Office of Air and Radiation's homepage on the Internet contains a wide range of information on air pollution programs and issues. The Office of Air and Radiation's homepage address is: (http://www.epa.gov/air/).

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