INFOTERRA: News: Debate Over Natural Oxidizing Capacity of Atmosphere Continues
Perhaps the story, below, should be read in the context of a phrase,
toward the end, suggesting that the author of the present study has had a
long and on-going debate with the author of a previous study, Ronald Prinn
of MIT, whose work had indicated that key chemical concentrations of
hydroxyl were in decline.
A piece on the Prinn study, pointing to some of the real difficulties of
attempting to research the issue, is at:
http://www.greeningearthsociety.org/climate/previous_issues/vol6/v6n20/hot1.htm
Ashwani
Vasishth vasishth@usc.edu
http://www-rcf.usc.edu/~vasishth
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http://enn.com/news/wire-stories/2003/01/01092003/ap_49318.asp
Natural atmospheric scrubber not in decline, study finds
Thursday, January 09, 2003
By Andrew Bridges, Associated Press
LOS ANGELES - A natural chemical that scrubs pollution from the sky is
more abundant than previously believed, leading scientists to wonder if
they have been underestimating the atmosphere's ability to cleanse itself.
A new study by European scientists shows levels of the chemical, hydroxyl,
are probably steady or even on the rise. Details appear Thursday in the
journal Nature.
The report contradicts a U.S. study published in 2001 suggesting hydroxyl
levels have dropped dramatically since 1990. The author of that report,
Ronald Prinn of the Massachusetts Institute of Technology, was out of the
country and unavailable for comment, his secretary said.
Hydroxyl, or OH, is important because it chemically reacts with a range of
polluting gases, including methane and carbon monoxide, and removes them
from the atmosphere.
The short-lived chemical is difficult to directly measure. Instead,
scientists measure concentrations of chemicals that react with it.
For years, the best proxy has been a banned industrial solvent called
methyl chloroform.
Since it was produced and used in known quantities until outlawed in 1987,
scientists compared its industrial output with its measurable presence in
the atmosphere. The difference between the two allowed the amount removed
by hydroxyl - and thus levels of hydroxyl itself - to be deduced.
The Prinn study was based on calculations that methyl chloroform emissions
had fallen to near zero.
Instead, measurements made over Europe in 2000 showed emissions of the
chemical have persisted, albeit in small amounts, despite the 1987 ban,
said Maarten Krol, of the Institute for Marine and Atmospheric Research
Utrecht, Netherlands.
The source is unknown, but could be waste products buried in European
dumps or the continued, illicit use of the solvent, Krol said.
The finding throws into doubt the theory that the cleansing capacity of
the atmosphere has been reduced, since hydroxyl concentrations would have
been further depleted had methyl chloroform levels fallen to zero.
"Maybe the dramatic stories about the collapse of the oxidizing capacity
of the atmosphere are based on false assumptions," said Krol, who has
debated the subject with Prinn for years.
Steve Montzka, a research chemist with the National Oceanic and
Atmospheric Administration in Boulder, Colorado, said Krol's paper showed
how the emissions assumptions underpinning Prinn's work may be flawed.
"Without any emissions, you would not need as much OH to explain the
changes observed in the atmosphere for methyl chloroform," Montzka said.
"With more emissions, it means you need more OH."
Copyright 2003, Associated Press All Rights Reserved More ENN news
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