Atmospheric carbon monoxide levels decreasing in mid-Atlantic region

September 07, 1999

Levels of atmospheric carbon monoxide (CO) are decreasing in the U.S. mid-Atlantic region, according to a new study by University of Maryland and National Park Service scientists. In a paper to be published in the September 15 issue of Geophysical Research Letters, they compare carbon monoxide concentration levels at Big Meadows in Shenandoah National Park, Virginia, in the periods 1988-1989 and 1994-1997. They report that the annual decrease amounts to around five parts per billion by volume (ppbv).

Air quality measurements and analysis were performed by Kristen A. Hallock-Waters, Bruce Doddridge, and Russell Dickerson of the University of Maryland at the Big Meadows site, which has long been accepted as representative of air quality in the mid-Atlantic region as a whole. Located at 1,100 meters (3,609 feet) altitude, Big Meadows is removed from local sources of pollution. In addition to carbon monoxide, sampled from a ten meter (33-foot) tower slightly above treetop level, the Big Meadows monitoring station observes weather conditions, ultraviolet light penetration, ozone, sulfur dioxide, and reactive nitrogen compounds in the air.

The researchers attribute the decrease in carbon monoxide largely to reductions in manmade emissions, consistent with trends in emissions reported by the U.S. Environmental Protection Agency (EPA) and other Northern Hemisphere research. Carbon monoxide is a trace pollutant in the troposphere, or lower atmosphere, and is released by the combustion of fossil fuels (such as gasoline) and by biomass burning (such as forest fires). It is an important link controlling the oxidizing capacity of the atmosphere, through its chemical interaction with the hydroxyl radical (OH).

The mean level of carbon monoxide at Big Meadows in 1988-1989 was 204 ppbv, as compared with 166 in 1997, a decrease of 4.8 ppbv per year or 22.9 percent total. EPA estimates that in the same time span, manmade carbon monoxide emissions decreased by 18.3 percent, with reduction in on-road vehicle emissions accounting for much of the decrease. The carbon monoxide levels are given as annual averages based on hourly samples, as there is considerable fluctuation from hour to hour and month to month.
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The study was supported by grants from the U.S. Department of the Interior, the National Park Service, and EPA, with additional funding from the National Science Foundation and the North American Research Strategy for Tropospheric Ozone--Northeast through the Electric Power Research Institute.

Notes for science writers: A copy of the paper, "Carbon monoxide in the U.S. Mid-Atlantic troposphere: Evidence for a decreasing trend," by Kristen A. Hallock-Waters, Bruce G. Doddridge, Russell R. Dickerson, Shane Spitzer, and John D. Ray is available on request to Harvey Leifert hleifert@agu.org. Please provide your name, publication, and fax number. The paper is not under embargo.

For further information on the science in this paper, journalists may contact:
Kristen Hallock-Waters kristen@atmos.umd.edu, 301-405-7625
Dr. Bruce Doddridge bruce@atmos.umd.edu, 301-405-7628
Dr. Russell Dickerson russ@atmos.umd.edu, 301-405-5364

American Geophysical Union

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