Late-Night Nitrates Produce Aerosols

Nitrate radical chemistry taking place during the wee hours can drive atmospheric aerosol formation, according to a report published in Science (DOI: 10.1126/science.1221520). So-called secondary organic aerosols that form in the atmosphere when oxidized organic compounds condense can affect air quality, weather, and climate. Laboratory experiments previously predicted that the chemistry of nitrogen oxides, which produce nitrate radicals, would affect secondary aerosol formation. But the effect had not been observed in nature. A research group led by Ronald C. Cohen of the University of California, Berkeley, tracked the organic nitrate content of particles in Bakersfield, Calif., and found that nitrate radicals led to 27 to 40% of nighttime aerosol growth. And that’s just tracking the nitrate group, Cohen says. “It’s reasonable to assume that there’s a parallel path that doesn’t keep the nitrate attached, so everything at night might be from nitrate radicals,” he adds. Cohen suggests that emissions controls on nitrogen oxides will reduce aerosol formation.