Cities with Less Smog See More Green

Thanks to the Clean Air Act, many metro areas have tackled poor air quality, saving thousands of lives and millions of dollars in the process

by Maya Roney

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As sunburn victims and Al Gore fans well know, we're short on stratospheric ozone these days. But ozone created near the ground—the primary component of urban smog—is one of the country's most widespread and most damaging air pollutants, and few are complaining about its gradual depletion.

Many metropolitan areas have successfully cracked down on their ground-level ozone pollution problems since the Environmental Protection Agency passed the Clean Air Act in 1990. Between 1990 and 2005, ground-level ozone concentration dropped 9.2% on average in the metro areas in which the EPA monitored these data.

Aggressive Reduction of Ozone

Orange County, Calif., reduced its "bad" ozone levels by more than 50% during this time period, rising from the fifth-worst metro area for air quality to the 39th best, out of 197 metro areas. Seattle cut ozone pollution by 43% and San Diego saw a 42.5% decrease. On the East Coast, Atlantic City, N.J., decreased ozone levels by 37% between 1990 and 2005, and ozone pollution in the New London (Conn.) area dropped more than 35%. These measurements are based on the second-highest reading in each area for each year (researchers disregard the highest reading, which is often a fluke that could skew the data).

Unlike "good" ozone, which is produced naturally in the stratosphere (the part of the atmosphere 6–30 miles above the earth's surface), ground-level ozone is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) under the influence of sunlight. The chemicals involved come from emissions from industrial factories and electric utilities, motor vehicle exhaust, and vapors from oil wells and gasoline, paint, and other solvents.

Many cities and suburbs in the U.S. suffer from high levels of bad ozone due to the high concentration of motor vehicle traffic and industry in those areas, but even rural areas can be subject to high ozone levels as winds carry emissions hundreds of miles away from their original source, according to the EPA. The metro areas with the highest ozone pollution levels (based on second-highest annual readings) are Danbury, Conn.; New Haven, Conn.; Riverside, Calif.; and Wilmington, Del. Ozone levels are lowest in Honolulu; Santa Cruz, Calif.; Santa Rosa, Calif.; and Bellingham, Wash.

Evidence from Atlanta Olympics

While stratospheric ozone protects people from the sun's harmful ultraviolet rays, ground-level ozone triggers and aggravates all kinds of respiratory problems. It can cause coughing, chest pain, and throat irritation, and worsen conditions like asthma, emphysema, and bronchitis. "It's like getting a sunburn on your lungs when you inhale," says Janice Nolen, assistant vice-president for the American Lung Assn.

The 1996 Summer Olympic Games in Atlanta allowed researchers at the Centers for Disease Control & Prevention a rare opportunity to observe the impact of ozone on respiratory health. During the Olympics, Atlanta implemented a number of measures to reduce traffic, including providing 24-hour public transportation, adding an additional 1,000 city buses to its existing fleet, and closing downtown streets to all but public transportation vehicles. In the two-week period, the study found that peak ozone levels dropped by more than 25% and Medicaid expenses for asthma were cut by 40% as hospitalizations for asthma attacks decreased.

Under the 1990 Clean Air Act, the EPA now monitors air quality across the country and sets and reviews national air-quality standards for ozone to protect public health. Ozone concentration is measured in parts per million (ppm), the number of molecules of ozone (O₃) per every 1 million molecules of other gases that make up the air. The peak levels for each hour are averaged for the day. The EPA's standard for the second-highest daily average in a given year was 0.125 ppm until 1997, when the standard was tightened to 0.08 ppm for the fourth-highest daily average. Only the seven worst metro areas in the U.S. exceeded the original "second-max" ozone standard in 2005.