Page 61 - Air Pollution Control Engineering

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Fig. 16. Tropospheric ozone formation. (From US EPA.)

Other negative impacts are associated with ozone exposure, such as materials sus-
taining damage from ozone exposure. The useful life of synthetic and rubber compounds
become significantly shorter when they are exposed to ozone-laden environment.
Additionally, reduction in crop fields, lower forest growth rate, and premature leaf
droppage may occur from ozone exposure. The US EPA has estimated that the dam-
age to commercial crops and forests resulting from ozone exposure ranged between 2 and
3 billion dollars. Reduction in visibility by photochemical smog can also be considered as
a negative impact on society.
As established under the Clean Air Act (CAA), the air quality standards for air pollu-
tants including ozone are the responsibility of the US EPA. To illustrate the extent of the
ozone problem in the United States, one can compare the health-based ambient air quality
standard with the air-quality-monitoring data reported for areas throughout the United
States. Based on an hourly average not to be exceeded more than once annually, the
national ambient air quality (NAAQ) standard for ozone is 0.12 ppm. When this ambi-
ent air standard is compared to historical monitoring data, over 60 areas nationwide
have routinely exceeded this standard. It is estimated that over 100 million people live
in these areas. However, recent data have indicated that ozone levels have shown some
improvement in these areas, but the ambient air quality standard for ozone is still being
exceeded in many areas that contain a significant portion of the total population of the
United States. It has been determined that some these areas may not attain the ambient
air quality standard for many years. To address these “nonattainment” areas, Congress
amended the CAA in 1990. These nonattainment areas do not attain the ambient air
quality standards for several criteria pollutants, include ozone. The amendment