Research from Germany has found that the high particulate numbers in smoggy areas increase the risk of stroke. The Heinz Nixdorf Recall study followed more than 4,400 people between the ages of 45 and 74 years old.

The researchers began the study in 2000. They compared stroke and heart attacks to air pollution particulate matter (PM) levels of PM10 (particle sizes of 10 micrometers or less) and PM2.5 (2.5 micrometers or less).

The study found that stroke incidence was more than two-and-a-half times higher among people with long-term exposure to PM10, while stroke incidence increased by more than three times among people with long-term exposure to PM2.5 smog.