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MIT researchers build model simulating atmospheric transport of PAHs; how chemicals get to the Arctic

MIT researchers have built a model to simulate long-range atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). The model that will be further developed as part of an NSF-funded project to track how chemicals get to remote Arctic environments.

Persistent organic pollutants are chemicals of substantial international concern. For emerging contaminants in the Arctic, we need to know more about their sources, environmental behavior, and transport pathways in order to regulate them more effectively.

—Noelle Selin, lead researcher

Selin, and assistant professor in MIT’s Engineering Systems Division and Department of Earth, Atmospheric and Planetary Sciences, and Carey Friedman, a postdoctoral associate at the MIT Joint Program on the Science and Policy of Global Change, had their latest results published in the ACS journal Environmental Science & Technology.

Selin and Friedman use the global 3-D chemical transport model GEOS-Chem to track the day-to-day transport of PAHs—toxic byproducts of burning wood, coal, oil and other forms of energy that remain in the atmosphere for less time than other persistent organic pollutants regulated by global standards.

GEOS-Chem captures observed seasonal trends with no statistically significant difference between simulated and measured mean annual concentrations. GEOS-Chem also captures variability in observed concentrations at non-urban sites (r = 0.64, 0.72, and 0.74, for PHE, PYR, and BaP). Sensitivity simulations suggest snow/ice scavenging is important for gas-phase PAHs, and on-particle oxidation and temperature-dependency of gas-particle partitioning have greater effects on transport than irreversible partitioning or increased particle concentrations. GEOS-Chem estimates mean atmospheric lifetimes of <1 day for all three PAHs. Though corresponding half-lives are lower than the 2-day screening criterion for international policy action, we simulate concentrations at the high-Arctic station of Spitsbergen within four times observed concentrations with strong correlation (r = 0.70, 0.68, and 0.70 for PHE, PYR, and BaP). European and Russian emissions combined account for ∼80% of episodic high-concentration events at Spitsbergen.

—Friedman and Selin

Friedman’s work will provide a foundation for ongoing work in Selin’s research group at MIT, in collaboration with the University of Rhode Island and the Harvard School of Public Health. Together the researchers will be exploring the global transport of other contaminants in the Arctic, such as chemicals used in stain-resistant carpets and non-stick pans. In research going forward, Selin and her team will extend the model created in their recent analysis that allows them to track chemicals with much greater precision.

The presence of these pollutants in the Arctic is important for several reasons. First, the researchers say there’s a very real health concern. Organic pollutants typically condense and rain down into Arctic regions. Once they mix with other chemicals, it’s unknown what danger they could pose to animals and humans, especially in concert with climate change stressors in the Arctic. These chemicals are already known to build up in the fat of whales, seals and other animals—a main source of food for people living in these high latitude regions.

At the same time, the practices that create some of these chemicals such as gas and oil exploration and shipping are expected to increase in the Arctic. As they do, it’s important to understand how pollutants traveling from distant sources exacerbate the problem, and how climate changes can affect future contamination, the researchers say.

Climate change and contaminants are both substantial present and future threats to the Arctic, and our research can ultimately help leaders make better policies to protect this unique environment

—Noelle Selin


  • Carey L. Friedman and Noelle E. Selin (2012) Long-Range Atmospheric Transport of Polycyclic Aromatic Hydrocarbons: A Global 3-D Model Analysis Including Evaluation of Arctic Sources. Environmental Science & Technology 46 (17), 9501-9510 doi: 10.1021/es301904d


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