The U.S. Environmental Protection Agency announced a proposal Thursday to strengthen the nation's air quality standard for ground-level ozone.
The EPA recommended an ozone standard within a range of 0.070 to 0.075 parts per million, as well as soliciting comments on alternative standards within a range from 0.060 ppm up to the level of the current 8-hour ozone standard, of 0.08 ppm.
EPA scientists said ground-level ozone -- the primary component of smog -- is not emitted directly into the air but is created through a reaction of nitrogen oxides and volatile organic compound emissions in the presence of sunlight. Major man-made sources include emissions from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents'
The EPA also proposed revising the "secondary" standard for ozone to improve protection for plants, trees and crops during the growing season. The secondary standard is based on scientific evidence indicating exposure to even low levels of ozone can damage vegetation.
The agency said it will have public hearings on its proposals: Aug. 30 in Los Angeles and Philadelphia and Sept. 5 in Chicago and Houston.
Copyright 2007 by United Press International
Explore further: 14 states sue to allege US failure to enforce smog rules