GRANTS PASS, Ore. - Ozone blowing over from Asia is raising background levels of a major ingredient of smog in the skies over California, Oregon, Washington, and other Western states, according to a new study appearing in today’s edition of the journal Nature.
The amounts are small and, so far, found only in a region of the atmosphere known as the free troposphere, at an altitude of 2 to 5 miles, but the development could complicate US efforts to control air pollution.
Though small, the levels have risen steadily since 1995, and probably longer, said Owen R. Cooper, lead author and a University of Colorado research scientist attached to the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo.
“The important aspect of this study for North America is that we have a strong indication that baseline ozone is increasing,’’ said Cooper. “We still don’t know how much is coming down to the surface. If the surface ozone is increasing along with the free tropospheric ozone, that could make it more difficult for the US to meet its ozone air quality standard.’’
The study is the first link between atmospheric ozone over the United States and Asian pollution, said Dan Jaffe, a University of Washington-Bothell professor of atmospheric and environmental chemistry.
He contributed data from his observatory on top of Mount Bachelor in Oregon to the study.
The US Environmental Protection Agency is considering whether to lower the current limit on ozone in the atmosphere by as much as 20 percent and is working with China to reduce its emissions of the chemicals that turn into ozone. Ozone is harmful to people and plants.