Asian, European Emissions Impact U.S. Air Quality

Up to 15 percent of U.S. air pollution comes from Asian and European sources, according to a study from the Nelson Institute for Environmental Studies at the University of Wisconsin-Madison.

"It is useful to understand how much air pollution is coming from areas outside our own region, so that when we're thinking about how to cut down ozone concentrations, we can take into account what factors we have control over and what factors we don't have control over," said Tracey Holloway, a professor of environmental studies in the Center for Sustainability and the Global Environment (SAGE), who led the new study.

Unlike the protective stratospheric ozone layer, surface ozone is a pollutant and has been implicated in increased mortality rates, respiratory and cardiovascular disease and vegetative and crop damage, the researchers said.

Using a computer model that analyzed global wind data and chemical emissions from various countries, the research group found that the impact of Asian and European ozone contributions varies across the country.

While previous computer modeling studies have examined ozone transportation between entire continents, often focusing on spring and summer, Holloway said. "[Our study] is the first that has laid out the seasonality of ozone import to specific regions of the United States."

Overall, the models showed Asian and European emissions contributed three to 18 percent of total surface ozone on a monthly average basis across the United States. The western states endured the heaviest impact, due to their proximity to Asia and the predominance of west-to-east wind currents, Holloway said. Foreign emissions contributed an annual average of 12 percent of the total surface ozone along the West Coast, but only six to ten percent along the East Coast.

Spring and fall peaks of imported ozone were evident in all regions as a result of the optimal combination of a strong jet stream across the Pacific Ocean and stability of ozone during these seasons.

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