Acid-Rain Component May Be More Potent Pollutant than Previously Thought, UB Chemists Discover

BUFFALO, N.Y. -- University at Buffalo chemists have found that nitric oxide, a common air pollutant and one of the components of acid rain, is highly reactive with ethanol, potentially making the chemical an even more insidious pollutant than has been thought.

The UB team also found that the reactive site between a nitric oxide cation (a positively charged atom) and an alcohol will vary greatly depending on the extent of solvation, that is, how many solvent molecules surround the reactants, a fundamental finding that will help chemists better tailor chemical reactions in the lab.

The research is scheduled for publication in today's issue of the Journal of the American Chemical Society (Vol. 122, Issue 48, pp. 11887-11892).

Two years ago, the UB team was the first to discover that reactions occurring between nitric oxide and methanol within gas-phase clusters probably are creating harmful pollutants in the upper atmosphere.

"This new research shows that there also is a class of aerosol reactions occurring between nitric oxide and ethanol," said James F. Garvey, Ph.D., professor of chemistry at the University at Buffalo, and co-author on the paper with Dong Nam Shin and Robert L. DeLeon, also of the Department of Chemistry in the UB College of Arts and Sciences.

The findings indicate that because nitric oxide is reactive with the broad range of alcohols, it potentially is more potent than scientists had believed previously.

"It turns out nitric oxide is insidious because it engages in more than simple bimolecular reactions. It has its own unique chemistry inside of gas-phase clusters," said Garvey, "and that may be something environmental regulators will need to take into account."

He noted that the UB studies may provide a new direction for atmospheric field studies, where scientists identify and test pollutants in the upper atmosphere.

Garvey explained that in the upper atmosphere, pollutants are generated when the nitric oxide/ethanol clusters react with sunlight. In the laboratory, the UB team used laser light to generate mixed gas-phase clusters of nitric oxide/ethanol and used mass spectrometry to confirm that photochemical reactions were occurring.

In fundamental terms, the findings also provide chemists with added insight into how solvation can affect the course of a chemical reaction.

"Chemists want to be able to control where the chemistry occurs," explained Garvey. "These results provide us with a new way to do just that. It turns out that subtle changes in the solvent 'cage' around the reactants bring about huge changes in how and where the reaction occurs. As the number of solvent molecules increases, we saw a direct change in where the reaction was occurring on the ethanol."

The team was able to observe this by performing a labeling experiment in which they replaced some of the hydrogens on ethanol with a different form of hydrogen, known as deuterium, allowing them to closely follow the course of the reaction.

The research was funded by the National Science Foundation.