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Scientists at the University of Washington have discovered that nighttime air pollution — coming primarily from car exhaust and power plant emissions — is responsible for a major drop in nighttime pollinator activity. Nitrate radicals (NO3) in the air degrade the scent chemicals released by a common wildflower, drastically reducing the scent-based cues that its chief pollinators rely on to locate the flower. The findings, published Feb. 9 in Science, are the first to show how nighttime pollution creates a chain of chemical reactions that degrades scent cues, leaving flowers undetectable by smell. The researchers also determined that pollution likely has worldwide impacts on pollination.

Ice core data from Greenland shows why air pollution is dropping more slowly than sulfur emissions reductions. As cloud droplets become less acidic, the chemical reaction that turns sulfur dioxide into sulfate aerosol gets more efficient. The new results can improve the models that project air quality and climate change.