Soot fouls subway stations — and maybe lungs

In the New York City subway, it’s not just the trains that are crowded. Air in the underground stations used by more than 5 million passengers each day also is chockablock with teeny-tiny pollutants, researchers report.

The sooty pollution is called black carbon. It is a byproduct of the burning of diesel fuel. The subway trains, which run on electricity, aren’t responsible. Maintenance trains that share the same tracks — and burn diesel fuel — spew the tiny pollutant particles.

Researchers measured levels of black carbon in the air in underground stations along several subway lines. That pollution can reach levels seven times as high, on average, as those at street level.

Researchers knew the subway air was dirty. And it’s not surprising. Wheels grinding along metal rails, for instance, fill tunnels with steel dust. Until now, no one had measured the levels of soot. The pollutants can be inhaled deeply into the lungs. Breathing in too much can aggravate respiratory problems, such as asthma.

High levels of the tiny airborne particles also have been found at subway stations in European cities, such as Amsterdam and Helsinki. Still, New York City’s stations may be the most polluted. That’s one conclusion of the study reported early online November 19 in Environmental Science & Technology.

Power Words

asthma  A disease affecting the body’s airways,which are the tubes through which animals breathe. Asthma obstructs these airways through swelling, the production of too much mucus or a tightening of the tubes. As a result, the body can expand to breathe in air, but loses the ability to exhale appropriately. The most common cause of asthma is an allergy. It is a leading cause of hospitalization and the top chronic disease responsible for kids missing school.

black carbon   Particles of carbon that are released when fossil fuels, wood or other carbon-based materials are burned.

diesel fuel  Heavier and oilier than gasoline, this is another type of fuel made from crude oil. It’s used to power many engines — not only in cars and trucks but also to power some industrial motors — that don’t rely on spark plugs to ignite the fuel.

pollutant   A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

soot      Also known as black carbon particles,these are the residues of incompletely burned materials, from plastics, leaves and wood to coal, oil and other fossil fuels. Some particles can be quite small — mere nanometers in diameter. If inhaled, they can end up deep within the lungs.