Chemists Discover That Aerosol Clusters Play Larger Role In Generation of Air Pollution

BUFFALO, N.Y. -- Tiny aerosol particles in the upper atmosphere may act like highly efficient chemical reactors, playing host to incredibly complex reactions that can create carcinogenic by-products even from the combination of fairly benign reagents, according to a paper published today by University at Buffalo chemists.

The researchers discovered that since these particles or clusters can contain up to thousands or even millions of molecules, they actually may have an amplifying effect on the reactions, causing them to play a much larger role in polluting air than previously was understood.

The work, reported in the current (March 22) issue of the Journal of Chemical Physics, may give government and industry a better handle on just how air pollution forms.

"If you're going to regulate compounds in the upper atmosphere, you have to be able to show industry what it is that happens chemically in the upper atmosphere that makes certain ones generated at ground level harmful," said James F. Garvey, Ph.D., professor of chemistry in the UB College of Arts and Sciences and lead author.

While much research has focused on which compounds are being generated in the upper atmosphere, relatively little work has examined how they are generated.

Researchers generally have assumed that many pollutants form from simple reactions between two molecules that happen to bump together in the atmosphere.

Garvey and his co-authors, Dong Nam Shin, Ph.D., former post-doctoral researcher in the UB Department of Chemistry, and Robert L. DeLeon, Ph.D., UB adjunct associate professor of chemistry, decided to look at what happened when they created in their lab a gas-phase cluster of nitric oxide -- one of the most common industrial emissions -- and methanol, a combination known to be generated in the upper atmosphere.

"This was the first combination we looked at and indeed, when this nanodroplet was exposed to ultraviolet light, it exhibited chemical reactivity," said Garvey.

That was surprising, Garvey explained, since under normal conditions, nitric oxide would not be expected to readily react with methanol, a volatile organic compound. But when Garvey's lab generated these mixed gas-phase clusters, simulating the way that they occur in the atmosphere, the two not only reacted, but they did so quickly and repeatedly.

The result was nitrous acid and methyl nitrite, a known carcinogen.

"Our work is one of the first clear indications of a complex, atmospheric reaction occurring inside a gas-phase cluster," said Garvey. "It is the first time people have observed within a gas-phase cluster, nitric oxide reacting with an organic molecule to create an acid and a reactive carcinogen."

He noted that while atmospheric reactions of nitric oxide with oxygen and water are well-known, the UB research shows that new molecules, such as volatile organic compounds, may make nitric oxide an even more harmful pollutant.

"This is a brand-new chemical reaction that occurs only inside these clusters," said Garvey, a fact that he noted hopefully will attract more attention to the role that these clusters play in air pollution.

"This is only the tip of the iceberg," said Garvey. "It leads us to believe there may be a rich family of reactions occurring in the atmosphere between nitric oxide and a variety of volatile organic compounds, such as alcohols, ethers and ketones, which go on to generate complex pollutants."

The research was supported by a National Science Foundation grant.