The city’s not just on your mind — it’s in it

Take a deep breath. If you live in an urban area like New York City, tiny flecks of iron ore known as magnetite are now traveling on the nerve that stretches from your nose to your brain, according to a new study in the Proceedings of the Natural Academy of Sciences. This particle isn’t a welcome commuter. It’s one of many tiny air pollutants that scientists have identified as potential risk factors for neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease, though this association is not fully understood.

Cities generate magnetite and other pollutants as they generate power — through combustion. Car engines and household boilers release magnetite particles as they burn oil. Even the friction between brake pads produces enough heat to liberate magnetite.

The new research marks the first time scientists clearly identified that the magnetite particles in the brain came from air pollutants, rather than from inside the body. Only magnetite particles that are smaller than 200 nanometers in diameter, which is hundreds of thousands of times smaller than a human hair, can travel from your nose through the olfactory nerve to your brain. These nerves have less of the barrier that protects other parts of the brain. The olfactory bulb, the part of your brain that receives signals from this nerve, is more inflamed in people who live in polluted areas, according to other research.

Researchers have found a variety of results when they test whether air pollution and Alzheimer’s are related; it is clearly linked with some proteins that are associated with Alzheimer’s, but not others. A study of more than one million people in Taiwan found that higher levels of air pollution correlated with a higher incidence of Alzheimer’s.

If you’re a concerned New Yorker, you can look at the city’s levels of particulate matter here, and compare them to the rest of the country. The national goal for particulate matter levels set with the Clean Air Act is about 12.5 micrograms per cubic meter, averaged over a year.

While New York is more polluted than, say, Montana, it has far better air quality than many cities around the world and has taken measures to reduce air pollution, including tough restrictions on soot and other pollution from cars, water heaters and generators. Those rules have paid off: concentrations of tiny (smaller than 2.5 micrograms) particles in New York’s air fell 16 percent between 2008 and 2014.

You may want to take deep, calming breaths in order to deal with the news that tiny magnetic particles are taking a nervy route from your nose to your brain. However, if you live in a city, you’ll need another coping method.