The risk of ischemic stroke – which results when a blood clot travels to the brain – increases with a rise in particulate air pollution, according to a study in Stroke: Journal of the American Heart Association. Led by researchers at Beth Israel Deaconess Medical Center (BIDMC) and the Harvard School of Public Health (HSPH), the findings are described in the October 27, 2005 on-line rapid access issue of the journal. The study, which examined the air quality on a total of 37,000 days in nine separate cities, found that risk of hospitalization for ischemic stroke was one percent higher on days with relatively high levels of air pollution, compared with low-air pollution days, according to lead author Gregory Wellenius, Sc.D., postdoctoral fellow in cardiology at BIDMC.