Washington: Older women might wonder why they are unable to recall names or places or where they keep their things. Chronic exposure to particulate air pollution might be to blame, says a new finding.

Such women, exposed to higher levels of ambient particulate matter over long term, experienced more decline in their cognitive functioning (process by which one becomes aware of, perceives or comprehends ideas) over a four-year period.

Higher levels of long-term exposure to both coarse and fine particulate matter, usually suspended in air, were linked with significantly faster cognitive decline.

Fine particulate matter are small particles, 30 times thinner than human hair, while coarse particulate matter are four or five times the size size of fine particles.

Exposure to particulate matter is also tied with cardiovascular risk, which itself may play a role in causing or accelerating cognitive decline, the journal Archives of Internal Medicine reports.

Jennifer Weuve, assistant professor of internal medicine at Rush University Institute of Healthy Aging and the principal study investigator, with colleagues evaluated air pollution, both coarse and fine, bearing on cognitive decline in older women. The study involveed 19,409 women aged 70 to 81 years over a 14-year period.

"Our study explored chronic exposure to particulate air pollution in relation to decline in cognitive functioning among older women," said Weuve.

"Very little is known about the role of particulate matter exposure and its association with cognitive decline," said Weuve, according to a Rush statement.

"Unlike other factors that may be involved in dementia such as diet and physical activity, air pollution is something we can intervene on as a society at large through policy, regulation and technology," said Weuve.

This is the first study to examine change in cognitive function over a period of time and whether exposure to the size of particulate matter is important.