Asian emissions affect US ozone levels

Nature : The phenomenon of pollution crossing the Pacific Ocean has been documented since the 1990s. Using chemical modeling to distinguish between locally produced and imported pollution, Meiyun Lin of Princeton University and colleagues analyzed air-quality data from satellites and ground measurements. They tracked the passage of ozone from Asia to the western US over the course of several days in mid 2010. Although the majority of pollution came from US sources, up to 20% of it came from Asian emissions. And on days when US cities had higher than the maximum allowable ozone levels, Asian emissions were what pushed them over the limit more than half the time. The findings, published in the Journal of Geophysical Research , have significant implications for the often volatile negotiation of international emissions standards.