Posted on 03/13/2003 7:12:11 AM PST by Isara
Coniferous forests may produce more smog components than traffic does, calculations suggest
Maybe Ronald Reagan was right after all about trees being big polluters. A new study suggests the Scotch pine and other northern evergreens may emit more nitrogen oxides -- key components of smog -- than all the cars and industrial plants on the planet.
It has been known for years that some plants emit small amounts of nitrogen oxides. Now, a team of Finnish and U.S. researchers has found that Scotch pine needles increase those emissions substantially when they are exposed to ultraviolet radiation from the sun. This led the researchers to make a provocative calculation.
"Our findings suggest that global nitrogen-oxides emissions from boreal coniferous forests may be comparable to those produced by worldwide industrial and traffic sources," says the paper, published in today's edition of the British journal Nature.
This would have delighted Mr. Reagan, the former U.S. president now incapacitated by Alzheimer's disease. Environmentalists ridiculed him in the early 1980s for declaring that "trees cause more pollution than automobiles."
Although he grossly overstated the case for plants as polluters, Mr. Reagan's so-called "killer tree" statement was based on science.
In the mid-1960s, U.S. researcher Reinhold Rasmussen, intrigued by the blue haze or atmospheric mist over Virginia's Blue Ridge Mountains, published the first paper making the connection between trees and smog. Ten years ago, other researchers began building on his work, and the United States Environmental Protection Agency is studying trees' contribution to pollution in the southeastern U.S.
But Mr. Reagan's mistake, at least with nitrogen oxides, was in saying that trees cause air pollution. Trees emit nitrogen oxides, but they are recycling what is already in the atmosphere, not producing more, said William Munger, a Harvard University atmospheric scientist and co-author of the Nature paper.
In other words, trees are not like cars. One hundred years ago, concentrations of nitrogen oxides in the atmosphere were far lower, Dr. Munger said. A little bit of them is produced naturally, by such things as lightning strikes and forest fires.
"The industrial world has made huge changes in that amount," he said.
This means that trees are probably recycling more nitrogen oxide. But that may not create smog, perhaps because the other chemical components aren't readily available. Tests in northern Quebec, for example, have found low levels of smog in the forests.
Recent work in Greenland found that snow also emits nitrogen oxides. Again, the snow is recycling the gas, not producing it, Dr. Munger said. (This is good news for Canada, as it is rich in both snow and evergreens.)
Researchers don't know much about how nitrogen-oxide cycling works, so the finding that sunlight is involved is significant, he said.
Kevin Percy, a researcher at the Canadian Forest Service, agrees that the finding is interesting. But he is not sure it is correct to assume that all evergreens produce nitrogen oxides.
He said the study's researchers may have overestimated the number of Scotch pines in the world -- the trees are common in Northern Europe, but in Canada's boreal forests, black spruce and trembling aspen predominate -- and may have been bombarding the pine needles with high levels of ultraviolet radiation not found in most of Canada.
Is the second half of the article true?
We need to eliminate cars!
No, I mean trees!
No, I mean cars!
No, I mean trees!
TIPPER!
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