Smog In Western U.S. Starts Out As Pollution In Asia, Researchers Say

"The U.S. is producing less air pollution, but smog levels are still rising in the western U.S. because of pollutants released in Asian countries that then drift over the Pacific Ocean. Researchers say their findings show the importance of a global approach to preserving air quality."

"'Scientists found Asian air pollution contributed as much as 65 percent of an increase in Western ozone in recent years,' NPR's Rob Schmitz reports from Shanghai. 'China and India, where many consumer products are manufactured, are the worst offenders.'"

"The problem, scientists say, is that Asian countries' emissions of nitrogen oxides — which sunlight then breaks down in reactions that produce ozone — have tripled since 1990. When those harmful gases circulate to North America, they offset gains in U.S. air quality that have come from cutting nitrogen oxide emissions by 50 percent."