When federal standards were set for carbon monoxide pollution in 1971, more than 90 percent of the locations with carbon monoxide monitors were in violation. But today the number of monitors showing violations has fallen to only a few, on a small number of days and mainly in areas with unique meteorological and topographical conditions. For example, in Fairbanks, Alaska, which has these unique conditions and where carbon monoxide limits were exceeded on more than 100 days per year in the 1970s, there has not been a violation in the last two years. National emissions standards for new cars and pickup trucks -- which are responsible for most carbon monoxide pollution -- were the main reason for the drop in carbon monoxide levels because they led to better emissions controls in these types of vehicles.
The regulation of carbon monoxide has been one of the great success stories in air pollution control, says a new report from the National Academies' National Research Council. Although a few areas that are still susceptible to accumulating high levels of the pollutant need to remain vigilant in controlling emissions and monitoring air quality, there is no need to tighten current federal carbon monoxide emissions standards on motor vehicles, the report adds.
The report was requested by Congress because of concern about the continuing vulnerability of a few locations to high carbon monoxide concentrations. These areas are subject to atmospheric "inversions," which are marked by temperatures that rise with altitude. When this occurs in areas with topographic features that keep wind speeds low, such as cities situated in basins, the combination prevents air circulation and the colder air -- along with carbon monoxide -- is trapped near the ground by the warmer air above.
Government officials in such locales can further reduce their risk of violating carbon monoxide standards by planning for worst-case combinations of high emissions and atmospheric inversions, the report says. They can complement federal vehicle-emissions standards with local measures such as vehicle inspection and maintenance programs that target high-emitting cars and pickups; the use of cold weather engine-block heaters that reduce the time before a vehicle's emissions-control catalyst is fully functional; and the use of low-sulfur gasoline that improves catalyst efficiency. Federal and state assistance should be provided to help implement such countermeasures in communities still at risk of violating carbon monoxide standards, the report adds.
Continued progress toward meeting the carbon monoxide standards in these at-risk locations will reduce the potential for adverse health effects from carbon monoxide pollution as well, the report notes. The main known health problem caused by this type of pollution is increased chest pain in people with coronary artery disease. In addition, studies have correlated high carbon monoxide concentrations with heart disease, childhood development abnormalities, and miscarriages; however, the report says there is insufficient evidence to prove that carbon monoxide is the sole cause of these other health problems since other air pollutants, such as particulate matter, are often present as well. The potential health risks from these other pollutants are a good reason for federal agencies to leave existing carbon monoxide monitors in place, even in areas not expected to violate standards, since carbon monoxide can indicate the presence of other pollutants, the report says. In places where carbon monoxide pollution may still be a problem, the public should be educated about its health effects and encouraged to participate in efforts to reduce emissions, the report says.
An additional benefit of more stringent emissions standards was revealed by a recent study from the Centers for Disease Control and Prevention, which showed that the stricter controls prevented 11,000 deaths from accidental carbon monoxide poisoning between 1968 and 1998.
The Research Council report was sponsored by the U.S. Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.