Springtime ozone increases over Western North America linked to emissions abroad

Jan 20, 2010
A cadre of government and commercial aircraft helped collect data for a new study linking an increase in springtime ozone levels in western North America with pollutants drifting eastward from overseas, including Asia. Credit: Image courtesy NOAA

Springtime ozone levels above western North America are rising primarily due to air flowing eastward from the Pacific Ocean, a trend that is largest when the air originates in Asia. These increases in ozone could make it more difficult for the United States to meet Clean Air Act standards for ozone pollution at ground level, according to a new international study. Published online Wednesday, Jan. 20, in the journal Nature, the study analyzed large sets of ozone data captured since 1984.

"In springtime, pollution from across the hemisphere, not nearby sources, contributes to the ozone increases above western North America," said lead author Owen R. Cooper, Ph.D., of the NOAA-funded Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. "When air is transported from a broad region of south and east Asia, the trend is largest."

The study focused on springtime ozone in a slice of the atmosphere from two to five miles above the surface of western North America, far below the protective ozone layer but above ozone-related, ground-level smog that is harmful to human health and crops. Ozone in this intermediate region constitutes the background or baseline level of ozone in the lower atmosphere. The study was the first to pull together and then analyze the nearly 100,000 ozone observations gathered in separate studies by instruments on aircraft, balloons, and other platforms.

Combustion of fossil fuels releases pollutants like and volatile organic compounds, or VOCs, which react in the presence of sunlight to form ozone. North American emissions contribute to global ozone levels, but the researchers did not find any evidence that these local emissions are driving the increasing trend in ozone above western North America.

Cooper and colleagues from NOAA's Research Laboratory in Boulder, Colo., and eight other research institutes used historical data of global atmospheric wind records and sophisticated computer modeling to match each ozone measurement with air-flow patterns for several days before it was recorded. This approach essentially let the scientists track ozone-producing emissions back to a broad region of origin.

This method is like imagining a box full of 40,000 tiny weightless balls at the exact location of each ozone measurement, explained Cooper. Considering winds in the days prior to the measurement, the computer model estimates which winds brought the balls to that spot and where they originated.

When the dominant airflow came from south and east Asia, the scientists saw the largest increases in ozone measurements. When airflow patterns were not directly from Asia, ozone still increased but at a lower rate, indicating the possibility that emissions from other places could be contributing to the ozone increases above North America. The study used springtime ozone measurements because previous studies have shown that air transport from Asia to North America is strongest in spring, making it easier to discern possible effects of distant on the North American ozone trends.

Ozone-measuring research balloons and research aircraft collected a portion of the data. Commercial flights equipped with ozone measuring instruments also collected a large share of the data through the MOZAIC program, initiated by European scientists in 1994. The bulk of the data was collected between 1995 and 2008, but the team also included a large ozone dataset from 1984.

The analysis shows an overall significant increase in springtime ozone of 14 percent from 1995 to 2008. When they included data from 1984, the year with the lowest average ozone level, the scientists saw a similar rate of increase from that time through 2008 and an overall increase in springtime ozone of 29 percent.

"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."

The influence of ozone from Asia and other sources on ground-level air quality is a question for further study, Cooper said. Scientists will need to routinely measure levels close to the surface at several locations along the West Coast to see whether similar trends are impacting ground-level air quality.

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jbl
not rated yet Jan 20, 2010
Sorry to be rather blunt, but: Duuhh. For those who have lived on the West coast for 20-30 years, the haze and pollutants have increased to the point where there are rarely clear days at all anymore. Even a casual look at a weather report satelite animation shows it coming from asia. It would be nice to see a comaritive analysis of respiratory illnesses such as bronchitis , asthma and other chronic illnesses. I would be reasonably sure that partilulates in the lungs of post-mortem autopsies could be directly linked to the rampant pollutants coming from the East.
pres68y
1 / 5 (1) Jan 21, 2010
Except the Asians already start with much polluted air coming from Europe.

Europe gets their much polluted air from what is crossing the Atlantic from the US.

Eastern US gets it from US out west... ad infinitum!

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