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Even though everyone knows that pollution is bad for the body, but you know the finer the particles of these compounds are, the worse they can be to your health. Effects include asthma, lung cancer and, as detected more recently, cardiac diseases.

Evidence suggests that exposure can also affect the brain, accelerating cognitive aging, leading to an increased risk of Alzheimer’s and other forms of dementia. The University of Southern California (USC) decided to measure these particles.

The measurement test. In an enclosed parking lot 100 m downwind of a busy US freeway, an aluminum hose sticks out the white trailer. Every minute, the hose sucks up hundreds of liters of air mixed with exhaust from the roughly 300,000 cars and diesel-burning freight trucks that rumbled by each day.

Crouched inside the trailer, a young chemical engineer named Arian Saffari, who works in the University laboratory, lifts the lid off a sooty cylinder attached to the holds – part of a sophisticated filtration system that captures and sorts pollutants by size. Inside is a scientific payload: sulfate, nitrate, ammonium, black carbon, and heavy metal at least 200 times smaller than the width of a human hair.

Toxicity and size of particles. The particles are too fine for many air pollution sensors to accurately measure, says Saffari, who works in a lab led by Constantinos Sioutas at USC. Typically smaller than 0,2 μm in diameter, these “ultrafine” particles fall within a broader class of air pollutants commonly referred to as PM2.5 because of their size, 2.5 μm or less.

When it comes to toxicity, size matters: the smaller the particles that cells are exposed to, Saffari says, the higher their levels of oxidative stress, such as peroxides, which can damage DNA and other cellular structures.

Controversy. The link between air pollution and dementia remains controversial. Even its proponents warn that more research is needed to confirm a causal connection and work out just how the particles might enter the brain and make mischief there.

But a growing number of epidemiological studies from around the world, new findings from animal models and human brain imaging studies, and increasingly sophisticated techniques for modeling PM2.5 exposures have raised alarms.

Indeed, in an 11 year epidemiological study published last year in Translational Psychiatry, USC researchers reported that living in places with PM2.5 exposures higher than the Environmental Protection Agency’s (EPA) standard of 12 μg/m³ nearly doubled dementia risk in older women.

If the findings hold up in the general population, air pollution could account for roughly 21% of dementia cases worldwide, says the study’s senior author, epidemiologist Jiu-Chiuan Chen, of the Keck School of Medicine at USC. Click here to read the full article.