Hitchhiking Pollution Rides on Cloud Seeds

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Pollution hitchhikes on airborne particles, enabling the chemicals created by forest fires and burning fossil fuels to travel beyond expectations. Without hitching a ride, most of these pollutants, known as polycyclic aromatic hydrocarbons (PAHs), would decay before reaching the extreme ends of the Earth.

The hitchhiking pollution seems to make traveling easier for their hosts as well. Secondary organic aerosols that carry pollutants last longer in the environment than their unencumbered kin. In one experiment, published in Environmental Science & Technology, the secondary organic aerosols impregnated with the pollutant pyrene lost less that 20 percent of their volume in 24 hours, compared to 70 percent in those without the pollutant.

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The mutually beneficial arrangement starts in the fiery cradle where both PAH pollutants and secondary organic aerosols form when carbon compounds in vegetation or fossil fuels are burned. The recent study found that secondary organic aerosols, which often seed clouds, are thick and viscous like tar. The goo encapsulates pollutants and protects them from degradation.

"What we've learned through fundamental studies on model systems in the lab has very important implications for long-range transport of pollutants in the real world," said physical chemist Alla Zelenyuk of the Department of Energy's Pacific Northwest National Laboratory in a press release. "In this study, we propose a new explanation for how PAHs get transported so far, by demonstrating that airborne particles become a protective vessel for PAH transport."

Together, the pollution and it's secondary organic aerosol can reach the Arctic where the pollutants collect in ice sheets and eventually enter the food chain. High levels of PAH toxins have been found in several Arctic species, including beluga whales (Delphinapterus leucas) and duck species (Polysticta stelleri and Histronicus histronicus). Humans who hunt Arctic animals are then exposed to the pollutants when they eat the wildlife.

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IMAGES: Emissions from the Syncrude Mildred Lake plant, north of Fort McMurray. The Alberta tar sands in Canada are the largest industrial project on the planet, and the world's most environmentally destructive. (Corbis)