Springtime ozone levels above Western North America are rising, and an in-depth study funded by the National Oceanic and Atmospheric Association (NOAA) shows that the cause originates from much further away.
"In springtime, pollution from across the hemisphere, not nearby sources, contributes to the ozone increases above Western North America," said lead author Dr. Owen R. Cooper at the University of Colorado at Boulder in a statement. "When air is transported from a broad region of south and east Asia, the trend is largest."
Cooper and colleagues from the NOAA’s Earth System Research Laboratory and members of eight other research institutes used global atmospheric wind records and computer modeling to match each ozone measurement with airflow patterns for several days before data was recorded. The approach let scientists track ozone-producing emissions back to a broad region of origin.
Scientists saw the largest increases in ozone measurements when dominant airflows came from South and East Asia.
When airflow patterns did not emanate directly from Asia, ozone still increased, but at a lower rate, indicating that emissions from other places could also be contributing to North American ozone increases.
While North American emissions do contribute to global ozone levels, researchers could not find any evidence showing that local emissions are responsible for ozone increases above Western North America.
"This study did not quantify how much of the ozone increase is solely due to Asia," Cooper said. "But we can say that the background ozone entering North America increased over the past 14 years and probably over the past 25 years."
Scientists say that there has been a significant increase of 14 percent in Western North America's springtime ozone from 1995 to 2008. These ozone increases could make it more difficult for the U.S. to meet Clean Air Act standards for ozone pollution at ground level.
Brandon Finley is a Research Associate at the University of Washington-Bothell. His university was one of several collaborating institutions in the study. His specialty is mercury. Dr. Dan Jaffe led the research but could not be reached for comment.
“Asia can take a lesson from the United States or Europe,” said Finley, who added that California had started programs to reduce smog with good effects. Asia could do the same.
He gave the examples of “smog checks on cars, scrubbers to reduce emissions from smokestacks” that could help air quality for people in Asia and indirectly benefit people in the Western U.S.
“Technology that seems very old to us, like scrubbing mercury from pilot plants, that would reduce heavy metal toxicity,” said Finley, who added that it would improve the health of those who live downwind.
“If you install materials in there that would reduce nitrous oxide, the precursor of ozone, though it costs money to install it they are effective. It would be to their population’s benefit. The people who live downwind are getting the highest doses of ozone.”
He said if Asian countries are able to improve their air quality they will benefit their own people and others in the world. Cooperation is essential.
Finley said he did not know what kinds of standards are in place for industrial emissions in Asia, but he thought they were not as strong as those in Europe and the U.S. In Asia, as here, costs are an obstacle.