Ozone is one of several key air pollutants of concern to human health.
Elevated concentrations of ozone can also harm plants. Fine particulate matter in the air can harm human health and impair visibility. Average concentrations increased more than 15 percent in five cities or counties, and decreased more than 15 percent in 38 cities or counties. Most had no or only insignificant change. About half of all individual monitoring sites are in violation of the recently promulgated federal standard.