The human being takes about 29,000 breaths a day and receives millions of airborne particles at each time. The biggest health problem is the particles that come from the burning of fossil fuels.

- What happens is that we breathe in ultra-fine particles. It can create inflammation in the lungs that then spreads to other organs in the body, says Michael Brauer, professor of public health science, in the world of science.

Getting into the brain

As we grow older, iron, called magnetite, naturally accumulates in the brain. Too much iron, on the other hand, is a sign of dementia. Geophysicist Barbara Maher has investigated how iron in exhaust gases can travel all the way into our brains, which can increase the risk of dementia.

- The particles we breathe in are so small that they can get through the nerve bundles. Then they come straight into the brain, says Barbara Maher.

The brain shrinks

A large Canadian study, comprising six million Ontario residents, shows that the risk of dementia increases by seven percent if you live less than 50 meters from a major road. Studies in the US show similar results.

- The brain shrinks when exposed to urban air pollution. Environmental exposure may be behind about ten percent of Alzheimer's cases in the United States, says Caleb Finch, professor of neurobiology, in the World of Science.

See "The Gift in the Air" in this week's Science World in SVT2 on February 24, 20:00 or on SVT Play from February 23.