Particulate Matter
Multiple recently released studies find a strong link between increased particulate matter air pollution and heart attacks. This recent study has found a clear correlation between the two.
To determine the average annual concentration of fine particulate matter for a particular city or county, visit the EPA's Air Trends Web site and look for "PM 2.5 Wtd AM" in the tables provided. The most recent data available from the EPA are from 2005.

