Mystery Ingredient Cleaning Earth's Atmosphere

Mother Nature has a previously unknown cleaning agent that scrubs away
toxic air pollution, scientists have discovered. the existence of the
still mysterious substance has shaken up decades-long assumptions
about our atmosphere's self-cleaning process. Many studies have shown
that trace gases and pollutants in the lowest level of our atmosphere
break down naturally, thanks to molecules called hydroxyl (OH)
radicals. But the breakdown spews out ozone, itself a toxic pollutant
and a greenhouse gas. Not so in China's heavily polluted Pearl River
Delta, where experts were stumped to find lots of OH radicals but
relatively small amounts of resulting ozone. Highly reactive OH
radicals are continually recycled in the atmosphere through reactions
with water vapor and nitric oxide, both naturally present in the air.
Part of nature's self-cleaning mechanism, the reactions break down
trace amounts of pollutants, said study co-author Franz Rohrer, of the
Institute of Chemistry and Dynamics of the Geosphere in Jülich,
Germany. But when the radicals are recycled by nitric oxide, ozone is
created. In the Pearl River region, about 37 miles (60 kilometers)
northwest of Guangzhou (Canton), OH radicals were more concentrated
than in any other place measured by the team worldwide, Rohrer said.
This suggests the existence of another method of recycling OH
radicals—one that occurs without nitric oxide, the team suggests in
this week's Science Express.
Such a process is so unexpected that scientists likely did not have
the right tools with them at the time to measure it, Rohrer said.The
team, led by Rohrer's colleague Andreas Hofzumahaus, plan to test
Chinese air samples in a simulation chamber in their laboratory.If
they can solve the puzzle, the yet unknown ingredient could have a
positive impact on the global atmosphere, Rohrer added.

http://news.nationalgeographic.com/news/2009/06/090604-air-pollution-self-clean_2.html