According to a post on the Green Car Congress blog, a University of Virginia study by funded by the National Science Foundation found that “air pollution from power plants and automobiles is diminishing the fragrance of flowers and thereby inhibiting the ability of pollinating insects to follow scent trails to their source. This could partially explain why wild populations of some pollinators, particularly bees, are declining in several areas of the world, including California and the Netherlands. ”

“The scent molecules produced by flowers in a less polluted environment, such as in the 1800s, could travel for roughly 1,000 to 1,200 meters; but in today’s polluted environment downwind of major cites, they may travel only 200 to 300 meters. This makes it increasingly difficult for pollinators to locate the flowers.” - Co-author Jose D. Fuentes, a professor of environmental sciences, at UVa.

The researchers believe that air pollution, especially during the peak period of summer, may be a factor. “To investigate this, they created a mathematical model of how the scents of flowers travel with the wind. The scent molecules produced by flowers are very volatile and they quickly bond with pollutants such as ozone, hydroxyl and nitrate radicals, which destroy the aromas they produce. This means that instead of traveling intact for long distances with the wind, the scents are chemically altered and the flowers, in a sense, no longer smell like flowers. This forces pollinators to search farther and longer and possibly to rely more on sight and less on smell.”

It quickly became apparent that air pollution destroys the aroma of flowers, by as much as 90 percent from periods before automobiles and heavy industry. And the more air pollution there is in a region, the greater the destruction of the flower scents.

Source: Quinn S. McFrederick, James C. Kathilankal and Jose D. Fuentes; Air pollution modifies floral scent trails; Atmospheric Environment Volume 42, Issue 10, March 2008, Pages 2336-2348 DOI: 10.1016/j.atmosenv.2007.12.033

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