Therese Mar, Ph.D., of the University of Washington in Seattle, notes that one of the major challenges in assessing the effects of air pollution on health is finding good air pollution exposure data, which are often unavailable. So she devised the "Stagnation Persistence Index," which calculates the number of hours in a 24-hour day in which wind speed is below the 5th percentile, or 1.5 miles per hour.
She collected data on deaths from various causes during the period of 1968 to 1995 in Seattle, and compared them with the Stagnation Persistence Index.
"We found that respiratory deaths and deaths from chronic obstructive pulmonary disease (COPD) increased 2 percent four days after an increase in the number of hours of stagnant air," Dr. Mar said. She also found a small but significant association between stagnant air and cardiovascular death 1 day after an increase in the number of hours of stagnant air.
One of the advantages of using wind data, she noted, is that it is readily available. "We can't always get air pollution data everywhere, but all cities have wind monitors," she said. "Also, particulate matter air pollution was not measured back in 1968, so this type of long-term analysis would not be possible using only air pollution data," she added.
Using wind data does not allow researchers to determine the specific type of pollution causing the increased risk of death, she noted.
Dr. Mar hopes to use the data from this study to see possible effects of environmental legislation. "In the future, we want to take this 28-year study period and look at different time frames, such as 1968-1971, before the Clean Air Act took effect, and then compare that data with subsequent years, to see if we can see a difference in mortality," she said. "We'd also like to find out if there is any association between mortality and stagnant air that is correlated with regulatory actions such as requirements for catalytic converters and burn bans for wood burning."