Mystery Ingredient Cleaning Earth's Atmosphere

Christine Dell'Amore, National Geographic News 4 Jun 09;

Mother Nature has a previously unknown cleaning agent that scrubs away toxic air pollution, scientists have discovered.

What's more, 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.

"It was a complete surprise to us [that], after such a long time of scientific research, such a big gap has been found," said study co-author Franz Rohrer, of the Institute of Chemistry and Dynamics of the Geosphere in Jülich, Germany.

Global Advantage

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, Rohrer said.

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.

Meanwhile, the delta's air contained relatively little ozone.

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.

"You have the advantage that the harmful pollutants are degraded fast, but you don't have the misfortune that ozone is generated for it," he said.

"You are gaining on both sides."

Big Change?

Jingqiu Mao, a postdoctoral research fellow at Harvard University's Atmospheric Chemistry Modeling Group, said there may be other explanations for the high level of OH radicals found in the Chinese delta.

But he added in an email that the new study's findings are different than all previous field-research results around the world.

"This paper will largely change our understanding of ozone production in many scales," Mao said, if the findings "can be confirmed by more evidences from field studies or laboratory experiments."