A common type of air pollution might speed up the mental decline that comes with aging, according to new research led by a Chicago scientist.

Particulate pollution, made of tiny particles and droplets from smokestacks and tailpipes, has been known to contribute to lung disease and other health problems. Now a study has linked higher exposure to it with cognitive deterioration.

Jennifer Weuve, an epidemiologist and assistant professor at Rush University’s Rush Institute for Healthy Aging, said each additional increment of exposure, defined as 10 micrograms of particulate matter per cubic meter of air, seems to age a person’s brain an extra two years. But she pointed out that, unlike other risk factors, air pollution is something public policy can tackle directly.

“These people, whose exposures that we reduce will experience a slower rate of cognitive decline, which means fewer people will reach the threshold of dementia during their lives,” Weuve said.

It’s not clear just how particulate pollution might speed up cognitive decline. It may have to do with increased rates of cardiovascular disease. But there also may be a direct mechanism: Some tiny particles can pass from the bloodstream into the brain.

Wueve’s study is large, based on a sample of 19,409 nurses. But some uncertainties remain. It’s difficult to tease out the effects of particulate pollution from other air pollutants that might come along with it. The pollution measures came from air quality monitoring in the area where each participant lived. The results are published in Archives of Internal Medicine.

This article has been chnaged to clarify the exposure increment linked to two years of aging.