Their findings may help unlock part of the mystery surrounding the current pollination crisis that is affecting a wide variety of crops. Scientists are seeking to determine why honeybees and bumblebees are dying off in the United States and in other countries, and the new study indicates that emissions from power plants and automobiles may play a part in the insects' demise.

Scientists already knew that scent-bearing hydrocarbon molecules released by flowers can be destroyed when they come into contact with ozone and other pollutants. Environmental sciences professor Jose Fuentes at the University of Virginia — working with graduate students Quinn McFrederick and James Kathilankal — used a mathematical model to determine how flowers' scents travel with the wind and how quickly they come into contact with pollutants that can destroy them. They described their results in the March issue of the journal Atmospheric Environment.

In the prevailing conditions before the 1800s, the researchers calculated, a flower's scent could travel from 3,280 feet to 4,000 feet, Fuentes said in an interview, but today, that scent might travel 650 feet to 1,000 feet in highly polluted areas such as Los Angeles or Houston.
This phenomenon triggers a cycle, the authors noted, in which the pollinators have trouble finding sufficient food, and as a result, their populations decline. That, in turn, translates into decreased pollination and keeps flowering plants, including many fruits and vegetables, from proliferating.

Fuentes said scientists now have a more sophisticated understanding of the signals for which insects are searching and that air pollution rapidly eliminates as much as 90 percent of flowers' aroma.

Since 2006, honeybee colonies in the United States have been suffering from a widespread phenomenon known as colony collapse disorder, in which adult worker bees abandon an otherwise-healthy hive.

John Burand, an associate professor at the University of Massachusetts at Amherst who is studying bee colony collapses, said the effects of air pollution described in the new study are probably not directly related to that phenomenon.

But, he added in an e-mail: "There is no doubt that air pollution and air quality is having an effect on bees and other pollinators. It appears there is more than one factor that is contributing to the (colony collapse disorder) phenomenon we are seeing with bees, and certainly air pollution in some fashion may be playing a role."