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Asian emissions can increase ground-level ozone pollution in U.S. West
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Asian emissions can increase ground-level ozone pollution in U.S. West

Contact: John Ewald, 240-429-6127

Springtime air pollution from Asia, swept across the Pacific Ocean on winds, can contribute to episodes of high surface ozone pollution in the western United States, according to a new study by NOAA scientists and academic colleagues.

Several recent studies have shown that powerful spring winds can carry Asian pollution into the atmosphere above North America. The new analysis goes further, using high-resolution models and observations to show how some of the imported pollution can descend to the surface, where it affects ground-level ozone, a regulated pollutant. At high concentrations, ground-level ozone can cause severe respiratory effects in some people, and it damages crops, trees, and other vegetation.

“We showed that Asian pollution directly contributes to surface ozone pollution episodes in parts of the western United States,” said Meiyun Lin, Ph.D., lead author of the new study. In several areas, about half of the springtime pollution episodes that exceeded federal limits would probably not have occurred without the contribution of Asian pollution, Lin said. Still, Asian pollution contributed to no more than 20 percent of the ground-level ozone, according to the new study: Other sources of the pollutant include local fossil fuel use, wildfires, and imported pollution from other regions of the globe.

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Lin is a researcher with NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) and the Cooperative Institute for Climate Science at Princeton University in New Jersey. The new paper is published online in the Journal of Geophysical Research – Atmospheres.

For the analysis, Lin and colleagues from NOAA’s Earth System Research Laboratory (ESRL); the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colo.; NASA, and the National Center for Atmospheric Research combined detailed observations with high-resolution modeling. The team drew upon data collected by balloon-borne instruments, aircraft, ground instruments, and satellites during an intensive study of air quality and climate in California in 2010.

The researchers found that NOAA GFDL’s high-resolution chemistry-climate model, AM3, could accurately reproduce the real-world pattern of ozone levels observed in California. And the model could differentiate the effects of local emissions – from vehicles, power plants and other factors – from Asian emissions.

During episodes of high surface ozone in parts of California and the Southwest, Asian emissions added 8 to 15 parts per billion of ozone to air, comprising up to 20 percent of the total. The Environmental Protection Agency’s health-based standard limits ozone to 75 parts per billion (averaged over 8 hours). Roughly half of the pollution episodes that exceeded that health-based standard would not have occurred – the study reported – without the addition of Asian pollution.

Finally, the scientists reported that they could use satellite data to predict when incoming plumes of polluted air might affect western air quality, one to three days ahead of time.

“Advance knowledge about incoming pollution could be helpful to local decision makers, who inform the public about episodes of poor air quality,” said Owen Cooper, Ph.D., coauthor of the paper and a researcher at ESRL and CIRES.


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