To estimate variability in global hydroxyl levels and thus the cleansing capacity of the atmosphere researchers turned to studying longer-lived chemicals that react with hydroxyl.
The industrial chemical methyl chloroform, for example, is destroyed in the atmosphere primarily by hydroxyl radicals. By comparing levels of methyl chloroform emitted into the atmosphere with levels measured in the atmosphere, researchers can estimate the concentration of hydroxyl and how it varies from year to year.
This technique produced estimates of hydroxyl that swung wildly in the 1980s and 1990s. Researchers struggled to understand whether the ups and downs were due to errors in emissions estimates for methyl chloroform, for example, or to real swings in hydroxyl levels. The swings would be of concern: Large fluctuations in hydroxyl radicals would mean the atmosphere's self-cleaning ability was very sensitive to human-caused or natural changes in the atmosphere.
To complicate matters, when scientists tried to measure the concentration of hydroxyl radical levels compared to other gases, such as methane, they were seeing only small variations from year to year. The same small fluctuation was occurring when scientists ran the standard global chemistry models.
An international agreement helped resolve the issue. In response to the Montreal Protocol the international agreement to phase out chemicals that are destroying the Earth's protective stratospheric ozone layer production of methyl chloroform all but stopped in the mid 1990s. As a result, emissions of this potent ozone-de
|Contact: Jana Goldman|