Jan. 21, 2010 -- WEDNESDAY, Jan. 20 (HealthDay News) -- Call it an unwanted gift from overseas: Scientists are reporting that springtime ozone levels above western North America are on the rise, in part because of air heading this way from Asia.
The boosts in ozone could make it hard for the United States to stay under pollution limits for ground level air set by the Clean Air Act, according to the researchers. Their report was published online Jan. 20 in Nature.
"This study did not quantify how much of the ozone increase is solely due to Asia, but we can say that the background ozone entering North America increased over the past 14 years and probably over the past 25 years," the study's lead author, Owen R. Cooper, of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder, said in a news release from the U.S. National Oceanic and Atmospheric Administration.
The research examined ozone during the springtime in the atmosphere from two to five miles above ground. That's below the ozone layer that protects the planet but above ground-level smog related to ozone. The study encompassed ozone observations from aircraft instruments and balloons, among other measurement tools.
The researchers found that ozone levels went up when the dominant airflow came from south and east Asia. They noted that emissions from North America also contribute to global ozone levels but said they found no evidence that local emissions were responsible for the ozone increases above the western part of the continent.
The findings focus on the years between 1995 and 2008, when most of the data were collected, but also include statistics from 1984.
Overall, springtime ozone in the region increased 14 percent since 1995 and 29 percent since 1984, the study reported.
The U.S. Environmental Protection Agency has more on ground-level ozone.
SOURCE: U.S. National Oceanic and Atmospheric Administration, news release, Jan. 20, 2010