New concern over added trace gases in the atmosphere
THERE'S been new concern about weakening earth's ozone in recent weeks. And newly reported research has confirmed a rapid buildup of methane in the atmosphere. Now it appears that the atmospheric concentration of carbon monoxide may also be on the rise. Human activity is polluting the atmosphere with a variety of gases. Their concentrations may range from only a few parts per million by weight to a few hundred p.p.m. - so dilute that meteorologists call them trace gases. Yet they are changing the chemistry of the atmosphere in ways that atmospheric chemists have only begun to understand.
But what they do understand of the probable action of these trace pollutants raises important environmental concerns.
Pollution by certain chemicals such as the chlorofluorocarbons used to cool refrigerators attacks the stratospheric ozone that absorbs harmful solar ultraviolet radiation. Carbon dioxide, released by burning fossil fuels, traps heat and can warm and change climate. The rising concentration of methane, due largely to increased human activity such as agriculture, adds a second heat-trapping gas.
Carbon monoxide (CO) pollution expands such concerns. Reaction with CO is the main way that an important, naturally generated chemical called the hydroxyl radical is lost from the atmosphere. These radicals, which are a combination of an oxygen atom and a hydrogen atom, remove many of the man-made pollutants. If a rise in CO reduces the availability of these scavengers, it will encourage an increase of the other trace gases.
In 1977, the United States' National Academy of Sciences called research on the global trend of CO concentration an urgent environmental need. M.A.K. Khalil and R.A. Rasmussen of the Institute of Atmospheric Sciences in Beaverton, Ore., responded to this challenge. In the March 17 issue of the international journal Nature, they report on systematic CO measurements made over the past six to eight years at sites from the Arctic Circle to the South Pole.
Their analysis shows a rate of increase in the globally averaged CO concentration of between 0.8 percent and 1.4 percent a year. They point out that CO trends are variable both from place to place and with time. So their results are somewhat uncertain. Nevertheless, they say, ``We believe that we have barely detected an increasing trend on global CO.''
CO comes from motor vehicle exhaust and other sources of incomplete combustion. Since these have been increasing, you would expect CO concentration to go up. As the Oregon scientists note, however, it will take ``a much longer series of systematic measurements'' than they have made to estimate CO trends accurately.
If the National Academy of Sciences thought it urgent to get such knowledge a decade ago, it is even more urgent today. We are changing the chemistry of our atmosphere rapidly and we better find out what we're doing to it.
A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.