May 12, 2005

Atmosphere may cleanse itself better than previously thought

WEST LAFAYETTE, Ind. – A research team from Purdue University and the University of California, San Diego has found that the Earth’s atmosphere may be more effective at cleansing itself of smog and other damaging hydrocarbons than was once thought.

Jamie Matthews
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Scientists, including Joseph S. Francisco, have learned that some naturally occurring atmospheric chemicals react with sunlight more effectively than previously thought to produce substances that "scrub" the air of smog. This group of chemicals, after absorbing energy from sunlight, is able to break down smog and other pollutants into far less harmful components.

While many such chemicals have long been known to behave in this way – producing natural air cleaners called OH radicals – the chemicals the team studied have for the first time been observed to produce air-scrubbing OH radicals at low ultraviolet wavelengths. This observation has eluded science primarily because photochemistry at these wavelengths has been difficult to study.

"Thanks to an innovative laser technique that at last allows us to observe these chemicals in action, we now theorize that the atmosphere may produce up to 20 percent more OH radicals from these chemicals than we once thought," said Francisco, who is a professor of both earth and atmospheric sciences and chemistry in Purdue’s College of Science. "We now have a better understanding of an atmospheric process that could be giving our pollution-weary lungs more breathing room."

Francisco's research, which he performed at the University of California, San Diego with two of that institution's scientists, lead author Amitabha Sinha and graduate student Jamie Matthews, appears in this week's (May 9—13) online early edition of the journal Proceedings of the National Academy of Sciences. It will appear in the print edition on May 24 (vol. 102, issue 21).

Much air pollution consists of chemicals called hydrocarbons, which are produced when we burn organic matter such as wood or fossil fuels. The atmosphere has three main ways to cleanse itself of such pollutants, two of which are relatively direct: either water droplets in clouds absorb them and rain them out, or sunlight strikes them and the energy breaks the molecules apart.

"The third way is the one we are concerned with here, the way that involves breaking these hydrocarbons down chemically," Francisco said. "For that, the atmosphere relies on a reactive group of chemicals called OH radicals that attach themselves to hydrocarbon