ScienceDaily (Apr. 11, 2008) — Air pollution from power plants and automobiles is destroying the fragrance of flowers and thereby inhibiting the ability of pollinating insects to follow scent trails to their source, a new University of Virginia study indicates. This could partially explain why wild populations of some pollinators, particularly bees -- which need nectar for food -- are declining in several areas of the world, including California and the Netherlands.

http://www.sciencedaily.com/releases/2008/04/080410170413.htm