Ozone: Unsafe Even at Very Low Levels
16 February 2006
Even at very low levels, ozone—the principal ingredient in smog—increases the risk of premature death, according to a nationwide study to be published in the April edition of the journal Environmental Health Perspectives.
The study, sponsored by the EPA and the Centers for Disease Control, and performed by Yale University and Johns Hopkins, found that if a safe level for ozone exists, it is only at very low or natural levels and far below current US and international regulations. A 10 part-per-billion increase in the average of the two previous days’ ozone levels is associated with a 0.30 percent increase in mortality.
The current study builds on research published in November 2004 in the Journal of the American Medical Association, which was the first national study of ozone and mortality.
This study investigates whether there is a threshold level below which ozone does not affect mortality. Our findings show that even if all 98 counties in our study met the current ozone standard every day, there would still be a significant link between ozone and premature mortality.
his indicates that further reductions in ozone pollution would benefit public health, even in areas that meet regulatory requirements.—Michelle Bell, Yale School of Forestry & Environmental Studies, and lead investigator
Researchers found that even for days that currently meet the EPA limit for an acceptable level of ozone—80 parts per billion for an eight-hour period—there was still an increased risk of death from the pollutant.
An effort is now under way by the EPA to consider whether more stringent standards for ozone are needed. The agency is mandated to set regulations for ozone under the Clean Air Act. Ozone, a gas that occurs naturally in the upper atmosphere, is created in the lower atmosphere when vehicle and industrial emissions react with sunlight. Levels typically rise when sunlight and heat are highest in the summer.
A separate recent study by researchers from Georgia Tech found that large amounts of NOx—a major contributor to ozone formation—are being transported to North America from across the Pacific Ocean and could be contributing to significant increases in ozone levels over North America.
The research appeared in volume 33 of the journal Geophysical Research Letters.
It’s well-known that pollutants don’t always stay in the region in which they are produced. What’s not understood as well is where and when they travel. Finding this large amount of NOx traveling from across the Pacific is important because it will allow us to build better models so we can better understand how pollutants created in one region of the world are affecting the other regions.—Yuhang Wang, Georgia Institute of Technology
Wang, along with colleagues from Tech, the University of California, Irvine, and the National Center for Atmospheric Research studied data from the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment when they found much larger amounts of an array of chemicals, including NOx, and ozone than predicted by current models.
Formed when fuel burns at a high temperature, many of the sources of NOx are man-made, with automobile exhaust, electric utilities and industrial activity responsible for the bulk of human-produced NOx. The amount of NOx available largely determines how much ozone, a major component of smog, is produced in most regions of the atmosphere.
“The Exposure-Response Curve for Ozone and Risk of Mortality and the Adequacy of Current Ozone Regulations”; Michelle L. Bell, Roger D. Peng, and Francesca Dominici; Environ Health Perspect; doi:10.1289/ehp.8816
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