A new explanation for rising and falling concentrations of the atmospheric pollutant nitrous acid (HNO2 ) could help predict ‘smog days’. Nitrous acid is quickly destroyed by sunlight in the atmosphere, but nevertheless it can build up to detectable levels during the day, pointing to an unknown source.
The new study explains how HNO2 created at night (from chemicals in car exhaust) can bind to particles in soil and dirt and survive in the form of a salt. During the day, other reactions release the HNO2 back into the atmosphere, where it builds up faster than sunlight can destroy it.
The finding is important because HNO2 is a major source of the hydroxyl radical, a reactive species that destroys some pollutants while creating others. A better understanding of atmospheric chemistry could improve the prediction of ‘smog days’.
Original research paper published in Nature Geoscience on December 1, 2014.
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