"Several studies have found that these particles - at least some of them - can actually get into the brain where they can cause inflammation and might even trigger some of those microscopic changes that are typical of Alzheimer's Disease."

Or it may be a more indirect effect. Numerous studies have identified an association between air pollution and cardiovascular disease, and the cognitive decline may be a result of damage to the blood supply.

For example, research published in the same journal as Weuve's paper, the Archives of Internal Medicine, found a higher risk of stroke on days when there were more particulates in the air. The fine particles were mainly from vehicle exhausts.

And a new study in the journal of the American Medical Association, JAMA, combined results of 34 studies and found a statistically significant association between heart attack risk and a wide range of air pollutants, excepting ozone.

The researchers say that as a risk factor for heart attack, air pollution isn't as dangerous as things like smoking and high blood pressure, but on the other hand, air pollution, especially for those in urban areas and industrialized countries, is an unavoidable part of daily life.