The study involves air pollutants called particulates, in this case tiny particles 2.5 micrometers or less. They can settle deep into the lungs and are not coughed up like grit might be. They also often consist of dangerous heavy metals such as mercury or arsenic. the team used a survey run by the National Institutes of Health and AARP, looking at more than 500,000 volunteers aged 50 to 71 in six states and two large cities, Atlanta and Detroit. They used Environmental Protection Agency data that breaks down exposure to air pollution by county or city.