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Summer 2003 Vol. 3 No. 2



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Fairbanks, Alaska, at 40 below zero, ŠAlaska Stock Images

A Regulatory Success Story

Controlling Carbon Monoxide Pollution

Temperatures in the atmosphere usually drop as altitude increases, but in some settings -- though it may seem counterintuitive -- the reverse can occur. When this atmospheric inversion in temperature takes place in a valley or other location with minimal air circulation, warmer air up above keeps colder air down below, confined near the ground. It also traps pollution, making cities in these areas more susceptible to poor air quality.

A pollutant of particular concern, especially in the winter, is carbon monoxide, which at high-enough levels can aggravate chest pain for people already suffering from heart disease, and has been correlated with abnormal childhood development and miscarriage. The continued susceptibility of some locations to high carbon monoxide levels prompted Congress to ask a National Research Council committee to look at how effective federal standards and better emissions controls in new motor vehicles have been at reducing the pollutant.

Although the committee confirmed that some areas where inversions occur are still at risk for episodes of high carbon monoxide levels, it called the regulation of this pollutant one of the "great success stories in air pollution control," and said there was no need to tighten current federal standards for carbon monoxide emissions from motor vehicles. Even in Fairbanks, Alaska, where atmospheric inversions and a bowl-like terrain can block the dispersion of carbon monoxide in the air, there has not been a violation of national standards in the last two years. That is a significant drop from the 1970s, when Fairbanks violated the standards on average more than 100 days a year.

When the Clean Air Act first established national standards for carbon monoxide in 1971, more than 90 percent of the locations that monitored carbon monoxide were in violation. However, violations are rare today, in large part due to new controls on vehicle emissions.

The incomplete combustion of fuel in cars and pickup trucks is the main contributor to carbon monoxide pollution. When combustion takes place in a car engine, oxygen is added to fuel carbon, converting it first to carbon monoxide and then to carbon dioxide. But if there is insufficient oxygen or not enough time to oxidize the fuel, carbon monoxide escapes in the exhaust before it can be converted. New technologies, such as catalytic converters that provide additional oxidation and onboard computers that control the combustion process, have reduced carbon monoxide emissions.

State vehicle inspection and maintenance programs, especially those that target older cars, and low-sulfur gasoline that improves catalyst efficiency have also contributed to the reduction in carbon monoxide emissions. And in some cold-weather places, such as Fairbanks, the use of engine-block heaters helps motorists to warm up their cars faster, thus reducing the time before the emissions-control catalyst is fully functional.

Problem locales should continue to take advantage of countermeasures such as these, the committee said, adding that the communities should plan for the worst-case combinations of high emissions and atmospheric inversions. They will need to keep monitoring the air for unacceptable carbon monoxide levels as well. In fact, the committee recommended that carbon monoxide monitors be left in place even in areas not expected to violate standards, since carbon monoxide can indicate the presence of other pollutants that present a health risk, such as particulate matter.

The committee noted that another benefit of the tougher standards was revealed in a study last year by the Centers for Disease Control and Prevention. It showed that over a 30-year time span, the stricter controls prevented 11,000 deaths from carbon monoxide poisoning, which can occur accidentally when a person spends too much time in an unventilated car with a malfunctioning or blocked tailpipe.   -- Bill Kearney


Managing Carbon Monoxide Pollution in Meteorological and Topographical Problem Areas. Committee on Carbon Monoxide Episodes in Meteorological and Topographical Problem Areas; Board on Environmental Studies and Toxicology and Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies; and Transportation Research Board (2003, 214 pp.; ISBN 0-309-08923-9; available from the National Academies Press, tel. 1-800-624-6242; $50.00 plus $4.50 shipping for single copies).

The committee was chaired by Armistead G. Russell, Georgia Power Distinguished Professor of Environmental Engineering, Georgia Institute of Technology, Atlanta. The study was funded by the U.S. Environmental Protection Agency.



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Copyright 2003 by the National Academy of Sciences