Air Quality in U.S. Continues to Improve

Published September 1, 2003

The United States has made dramatic progress in reducing air pollution over the past few decades, and most American cities now enjoy relatively good air quality.

But polls show most Americans believe air pollution has grown worse or will become worse in the future. They also believe most people face serious risks from air pollution.

This disconnect between perception and reality is, in part, the result of environmental activists’ exaggerations of air pollution levels and risks, which make air pollution appear to be increasing when in fact it has been declining. State and federal regulatory agencies sometimes also resort to such tactics, and the media generally report those claims uncritically.

As a result, public fears over air pollution are out of proportion to the actual risks posed by current air pollution levels. There is widespread but unwarranted pessimism about the nation’s prospects for further air pollution improvements.

If people overestimate their exposure to and risk from air pollution, they will demand stricter, more costly air pollution regulation.

We face many threats to our health and safety, but have limited resources with which to address them. By devoting excessive resources to one exaggerated risk, we are less able to counter other genuinely more serious risks. People can make informed decisions about air pollution control only if they have accurate information about the risks they face.

Air Quality Successes

The Environmental Protection Agency (EPA) monitors ozone and other air pollutants at hundreds of locations across the United States.

EPA has two ozone standards. The first, known as the “one-hour standard,” requires that daily ozone levels exceed 125 parts per billion (ppb) on no more than three days in any consecutive three-year period. Ozone levels are determined based on hourly averages (hence the name of the standard).

EPA’s “eight-hour standard,” promulgated in 1997, is more stringent. It requires that the average of the fourth-highest daily, eight-hour average ozone level from each of the most recent three years not exceed 85 ppb.

In the early 1980s, half of the nation’s monitoring stations registered ozone in excess of the federal one-hour standard, and they averaged more than 12 such exceedances per year. But as of the end of 2002, only 13 percent of the stations failed the one-hour standard and they averaged just four exceedances per year.

Figure 1 displays national ozone trends and shows that even the most polluted areas of the country achieved impressive ozone reductions during the past 20 years. About 40 percent of monitoring locations currently exceed the more stringent eight-hour standard, but peak eight-hour ozone levels are declining in most areas.

The nation’s success with air quality extends beyond ozone to other pollutants. For example, between 1981 and 2000, carbon monoxide (CO) declined 61 percent, sulfur dioxide (SO2) 50 percent, and nitrogen oxides (NOx) 14 percent. Only two among hundreds of the nation’s monitoring locations still exceed the CO and SO2 standards. All areas of the country meet the NOx standard. For all three pollutants, pollution levels are well below EPA standards in almost all cases.

Airborne particulate matter (PM, also known as soot) has also registered large declines. PM2.5 (particles up to 2.5 microns in diameter) dropped 33 percent from 1980 to 2000, while the soot emissions rate from diesel trucks is down almost 85 percent since 1975.

This downward trend in pollution levels will continue. On-road pollution measurements show per-mile emissions from gasoline vehicles are dropping by about 10 percent per year as the fleet turns over to more recent models that start out and stay much cleaner than vehicles built years ago. Diesel truck emissions are also declining, albeit about half as fast.

Although motorists are driving more miles each year and population growth means more motorists on the roads, the increases in driving are tiny compared to the large declines in vehicle emission rates and will do little to slow progress on auto pollution.

Emissions from industrial sources will also continue to drop. Starting in 2004, EPA regulations require a 60 percent reduction in warm-season NOx emissions from coal-fired power plants and industrial boilers–the major industrial sources of ozone-forming pollution. The federal Clean Air Act requires a 20 percent reduction in PM-forming SO2 from power plants between 2000 and 2010. Those reductions are in addition to substantial declines in industrial NOx and SO2 emissions over the last 30 years.


Despite past success in reducing air pollution and the positive outlook for the future, polls show most Americans think air pollution is getting worse. For example:

  • A January 2002 Wirthlin Poll found 66 percent of Americans believe air pollution has gotten worse during the past 10 years, up from 61 percent two years before. A poll commissioned by Environmental Defense in 2000 found 57 percent of Americans believe environmental conditions have declined during the past 30 years.
  • Americans also believe environmental quality will decline in the future. The 2000 Environmental Defense poll found 67 percent of Americans believe air pollution will continue to get worse. Likewise, a March 2001 Gallup Poll found 57 percent of Americans believe environmental quality is deteriorating.
  • Most Americans also believe air pollution remains a serious threat to their health. Some 80 percent of New Yorkers rate air pollution a “very serious” or “somewhat serious” problem, as do 77 percent of Texans. When asked about the most serious environmental issue facing California, a 34 percent plurality chose air pollution, with “growth” coming in a distant second at 13 percent.

Why do most Americans “know” so much about air pollution that is not so? Americans consider liberal environmental groups the most credible sources of information on the environment, yet those activist groups consistently provide misleading information on air pollution levels, trends, risks, and prospects.

Americans also trust information from regulatory agencies, yet the agencies often paint a misleadingly pessimistic picture. At the same time, the media often provide extensive coverage of air pollution reports and press releases from liberal environmentalists and government regulators, yet the press reports rarely include critical examination or context on the claims those organizations make.

Inflating Air Pollution Exposure

In its report State of the Air 2003, the American Lung Association claimed that between 1999 and 2001, Los Angeles County averaged 35 days per year with ozone in excess of EPA’s eight-hour ozone benchmark of 85 ppb. Yet, as shown in Figure 2, none of the county’s 14 ozone monitors registered anywhere near that many ozone exceedances. Indeed, the typical Los Angeles County location averaged six exceedances per year–83 percent fewer than the report claims–while the most densely populated areas of the county never exceeded the EPA benchmark at all.

The American Lung Association derived its inflated value by assigning an ozone violation to the entire county on any day at least one location in the county exceeded 85 ppb. For example, if ozone was high one day in Glendora and the next day in Santa Clara, 50 miles away, the report counted two high-ozone days for all 9.5 million people in Los Angeles County. The logical fallacy here is obvious–it is like failing an entire class when one student does poorly.

The Public Interest Research Group (PIRG) took the American Lung Association’s techniques to the state level. In its 2002 report Danger in the Air, PIRG claimed California exceeded the eight-hour ozone benchmark on 130 days in 2001. Yet almost half of the state’s monitoring locations had no exceedances, while the average location had seven. Even the worst location in California had only about half as many ozone exceedances as PIRG claimed for the whole state. PIRG similarly claimed fictitiously large ozone problems for every other state it scrutinized.

Regulatory agencies often take a similar tack in reporting ozone levels. For example, EPA recently downgraded California’s San Joaquin Valley air district–a multi-county region–from “serious” to “severe” for the one-hour ozone standard. The change gave the region more time to attain the standard, but also required more stringent air pollution controls.

In a press release announcing the action, EPA stated, “Air quality data from 1997 through 1999 indicates the San Joaquin Valley experienced 80 days of unhealthy levels of ozone air pollution.” Yet Clovis, a suburb of Fresno and the most polluted location in the valley, had 40 days above the one-hour benchmark, while nearly half of the valley’s monitoring locations were in compliance with the one-hour ozone standard.

In the latest installment of its annual air pollution trends report, EPA claimed 133 million Americans breathe air that exceeds one or more federal air pollution health standards–mainly the tough new annual PM2.5 and eight-hour ozone standards. Yet EPA’s claim is a substantial exaggeration.

The agency classifies Clean Air Act compliance status at the county level. For example, if any air pollution monitor in a county registers ozone in excess of federal requirements, that county is classified as “non-attainment.”

Such regional classification often makes sense, because pollution can be transported many miles from its source. The problem arises because EPA also uses county non-attainment status when counting the number of people who “breathe polluted air.” Because only one location in a county need exceed an air standard for the entire county to be classified as non-attainment, many people in a non-attainment county might in fact breathe clean air. Indeed, this situation is the norm, rather than the exception.

Bucking the Trends

Air pollution, as noted earlier, has been on the decline for decades, and emission trends from vehicles and industrial sources promise pollution levels will continue to decline in the future. Yet activists have gone to great lengths to convince the public otherwise. One technique is to ignore long-term trends and instead highlight years in which air pollution levels rose when compared with the previous year.

For example, in Danger in the Air, PIRG reported a 23 percent increase in eight-hour ozone exceedances between 2001 and 2002, while a recent National Environment Trust press release proclaimed “new survey finds massive smog problem in 2002.” Ozone levels did indeed rise between 2001 and 2002, mainly because mild weather in 2001 made it an unusually low-smog year.

Despite a substantial overall decline in smog between 1990 and 2002, there were five years during this period in which ozone levels rose compared to the previous year in most parts of the country. Ozone levels are strongly affected by weather, which varies from year to year much more than pollution emissions do. Single-year changes in either direction cannot be used to infer long-term trends in air pollution.

The national average number of eight-hour ozone exceedances declined almost 50 percent between 1999 and 2000 because the weather in 1999 was unusually favorable to smog formation. That single-year change is as meaningless for inferring long-term trends as the rise in ozone between 2001 and 2002 highlighted by PIRG. Nevertheless, it is worth noting that large single-year decreases in air pollution have failed to inspire laudatory reports or press releases from environmental groups on the nation’s success in fighting pollution.

The Future Is Clear

Although often unacknowledged by environmentalists, America’s past success in combating air pollution actually occurred in spite of rapid growth in vehicle travel. For example, the substantial pollution reductions achieved since 1980 occurred at the same time that total vehicle miles increased 75 percent. But can improvements in vehicle pollution control keep pace with increased vehicle use?

On-road pollution measurements show average emissions from gasoline vehicles are declining by about 10 percent per year, even as SUVs make up an increasing fraction of cars on the road. (See Figure 3.) Because of technological advances, newer cars start out and stay cleaner as they age, when compared with previous models.

EPA regulations that take effect with the 2004 model year require additional reductions of 70 percent for hydrocarbons and 80 percent for NOx below current new-car standards, along with increased durability requirements. Similar regulations for diesel trucks require a 90 percent reduction in NOx and soot emissions starting in 2007, in addition to tougher NOx standards already implemented this year.

Data from vehicle inspection programs and on-road emission measurements show SUV emissions have been converging with those of cars since the late 1990s. EPA’s 2004 standards make no distinction between SUVs and compacts; Chevy Suburbans must meet the same low emissions requirements as Geo Metros. The growing popularity of SUVs will make no difference for future air quality.

Based on observed emission trends and the requirements of new regulations, per-mile emissions will decline about 90 percent during the next 20 years, as twenty-first century vehicles make up an ever-larger portion of the fleet. Thus, even if Americans drive 50 percent more miles 20 years from now (a greater increase than most metropolitan areas project), total emissions would still decline by 85 percent from current levels.

Despite the evidence of substantial ongoing emission reductions from all major pollution sources, the American Lung Association asserts in its State of the Air: 2003 report that “much air pollution cleanup has been stalled during the past five years” because of a lack of effort by EPA.

Getting Real on Air Pollution

Liberal environmental activists and regulators do not produce reports and press releases on air quality for their own sake, but to influence public opinion. The reports and regulatory activities described above were accompanied by substantial public relations efforts, often receiving coverage in many newspapers across the country.

In most of those articles, reporters did not compare regulators’ and activists’ claims to actual pollution data and did not provide information on past trends and future prospects that would put the claims in context. As a result, activists and regulators have contributed to Americans’ misperceptions on the state of the nation’s air.

The battle against air pollution is actually a great success story in environmental protection and public health. The worst air pollution problems have been greatly reduced or eliminated, while parts of the greater San Bernardino and Fresno-Bakersfield areas in California are the only places that still frequently exceed the new eight-hour ozone benchmark.

Rather than air pollution being a worsening national crisis, the vast majority of the country has attained the original federal standards, and only a few regions are still a substantial distance from meeting the tougher new standards. Recent trends in ozone and particulate levels and in pollution emissions, along with already-adopted new requirements, show air pollution will continue to decline.

Most Americans trust information from liberal environmentalists and government agencies. A 1999 poll commissioned by the American Lung Association found 90 percent of people trust environmental information provided by the association (59 percent of them a “great deal”), while 79 percent trust EPA. A 2002 poll commissioned by the Sierra Club found 57 percent of Americans trust environmental groups for information on environmental issues.

At least with respect to air quality matters, that trust is clearly misplaced.

Joel Schwartz is a senior fellow in the Environment Program at Reason Public Policy Institute. He is a former officer of the California Inspection and Maintenance Review Committee, a government body charged with evaluating California’s Smog Check program. This article is a condensed version of an article Schwartz first published in the Summer 2003 issue of Regulation magazine.