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New research finds a link between vehicle emissions and cognitive function in older people.

People who live in polluted cities can see the grit and dirt produced from vehicle engines but some of the most damaging emissions are only now starting to be understood. They're ultrafine particles that are way too small to be seen. Hundreds of these particles, placed side by side, match the width of a human hair and are primarily produced by combustion in diesel engines.

Harvard doctoral researcher Melinda Power says we now understand that ultrafines are a more significant problem than emission gasses or those large particles that make your skin dirty.

"They can actually get absorbed in through the surface of the lung, into your body, or they can travel straight up the olfactory nerves into your brain," says Power. "And so these particulates because they are so small have the potential to not only enter the body but then interact with the cellular machinery of the body as well."

To study the effects of this pollution on seniors and their cognition, Power took data from a study of older men who live in and around the Boston area. In addition to collecting health information, researchers gave the men tests that measured their thinking.

Then Power matched the data about the men to their addresses.

"People who live next to major roads are going to have much higher exposure to traffic related particulates than people who live further away," says Power. "The largest determinant of indoor air quality is outdoor air quality. So all of our houses have some exchange of air with the outside and what's outside will end up inside."

Power found that a doubling of traffic pollution was associated with having a lower scores on cognition tests, even lower than what would be expected with normal aging.

"And to give a sense of what that means, we know that as people age, cognitive test scores decline. So these side effects are similar to that observed for a difference in 1.9 years of age. So it is not insignificant of that."

She says there are only one or two other studies that look at the association between cognition and pollution. But she says she feels confident she's identified an important phenomenon that needs to be examined more thoroughly. She plans several more studies to do that.

Power's paper is published in the journal Environmental Health Perspectives.

olfactory: connected with the sense of smell 嗅覺的

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（來源：VOA 編輯：崔旭燕）