Amplified Trace Gas Removal in the Troposphere - Field study in China reveals unusually high production of hydroxyl radicals.
Via sciencenews , sciencemag , nature
Unidentified chemical reactions taking place in some polluted air may be a source of hydroxyl radicals, data from a new field study suggest.
Hydroxyl (OH) radicals result from a series of sunlight-stimulated reactions in the atmosphere involving ozone, nitrous acid and hydrogen peroxide. The highly reactive hydroxyl radicals, which typically persist in the air no more than one second before they combine with volatile organic chemicals and other gases, help the atmosphere cleanse itself, says Franz Rohrer, an atmospheric chemist at the Jülich Research Center’s Institute for Tropospheric Chemistry in Germany.
Field data gathered in China’s Pearl River delta during the summer of 2006 hint that unknown reactions taking place in some polluted air can generate substantial — and unexpectedly large — amounts of hydroxyl radicals, Rohrer and his colleagues report online June 4 in Science.
The team took round-the-clock measurements of various atmospheric constituents in a rural yet heavily populated area about 60 kilometers northwest of Guangzhou. In that area, pollutants wafting from nearby cities mix with volatile organic chemicals produced by local trees and other vegetation, says Rohrer. Atmospheric concentrations of unburned hydrocarbons are high, but levels of various nitrogen oxides (NOx) are low.
While analyzing the data, the researchers noted an unexpected surge in hydroxyl radical levels — but without the prerequisite increase in ozone levels that should have accompanied it — around noon each day. At their peak, hydroxyl concentrations measured about 15 million radicals per cubic centimeter, between three and five times that expected according to current models of atmospheric chemistry, the team notes. All together, the unknown source or sources of hydroxyl produced enough of the chemical to have boosted its concentration about 28 parts per billion each hour.
