Mitchio Okumura

Mitchio Okumura

A team of scientists led by researchers from the California Institute of Technology (Caltech) and NASA’s Jet Propulsion Laboratory (JPL) have fully characterized a key chemical reaction that affects the formation of pollutants in smoggy air. The findings suggest that in the most polluted parts of Los Angeles—and on the most polluted days in those areas—current models are underestimating ozone levels, by between 5 to 10 percent. The results—published in this week’s issue of the journal Science—are likely to have “a small but significant impact on the predictions of computer models used to assess air quality, regulate emissions, and estimate the health impact of air pollution, ” says Mitchio Okumura, professor of chemical physics at Caltech and one of the principal investigators on the research.

Until the last decade or so, it was thought that NO2 and OH combine only to make nitric acid, HONO2, a fairly stable molecule with a long lifespan in the atmosphere. “HONO2, or nitric acid, dissolves in rainwater, so that the molecules get washed away,” Okumura explains. “It’s basically a sink for these radicals, taking them out of the ozone equation and thus slowing down the rate of ozone formation.”

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