Wind-blown pollution high in the atmosphere can settle to ground level and contribute to air quality violations in the western U.S.
This USDA map shows seasonal mean of ambient ozone concentrations between 9 a.m. and 4 p.m. over the continental United States from 1 July to 31 September 2005. Areas shown in brown, orange and red can experience significant crop yield loss and damage to ecosystem function from ambient ozone.
By Summit Voice
SUMMIT COUNTY — Springtime air pollution from Asia, carried across the Pacific Ocean by strong west winds, sometimes raises ozone levels in western states to levels that exceed air quality standards, according to NOAA-led study.
The pollution is carried high in the atmosphere, but high-resolution models and observations showed 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.
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.
The research 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 scientists said the instrumentation and models could enable forecasters to predict incoming pollution several days in advance, vital information for public health officials charged with issuing pollution warnings.
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.
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