Cities with Less Smog See More Green

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.

from Business Week