Scientists have discovered that nighttime air pollution -- coming primarily form 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 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.