Air pollution is destroying the fragrance of flowers and inhibiting the ability of bees and other insects to follow scent trails to their source, according to a recent study by UVA researchers. This phenomenon could partially explain why wild populations of some pollinators, particularly bees, are dying off in several parts 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 cities, they may travel only 200 to 300 meters,” says Jose D. Fuentes, an environmental sciences professor and co-author of a study published in the March issue of the journal Atmospheric Environment. “This makes it increasingly difficult for pollinators to locate the flowers.”

The finding points up a troubling cycle in which pollinators have difficulty locating enough food and, as a result, their numbers wane. This, in turn, leads to decreased pollination and the populations of flowering plants, including many fruits and vegetables, fail to proliferate.

Earlier studies have shown that the populations of honeybees, bumblebees and butterflies have significantly declined in recent years. To investigate whether emissions from power plants and automobiles have been a factor, Fuentes and his team created a mathematical model of how the scents of flowers travel with the wind. The scent molecules produced by flowers are volatile and they quickly bond with pollutants such as ozone, hydroxyl and nitrate radicals, which destroy the aromas they produce. Bees and other pollinators are therefore forced to search farther and longer and may have to rely more on sight, which is generally poor, and less on their sense of 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,” says Fuentes. “And the more air pollution there is in a region, the greater the destruction of the flower scents.”