Hate pollution? The air may be cleaner on the Metro than in your car


Riding the Metro could save you from more than just exorbitant tabs at the pump and the occasional fit of road rage. It could mean breathing cleaner air on your way to work.

In a study of the air quality experienced by L.A. commuters, first place went to air collected on the Gold Line, which runs mostly aboveground. The Red Line, which runs underground, came in second.

The air quality for both is likely better than you’ll encounter if you’re driving on the freeway, the authors said.


Researchers at USC analyzed air samples from the Gold and Red lines and around the USC campus on weekdays between 9:30 in the morning and 1 pm from May 2010 through August 2010. Volunteer commuters riding the Metro spent about 25% of the time on the platform and 75% on the train to mimic the average commuter’s experience while riding the train. The researchers gave the volunteers special suitcases equipped with tools to collect pollutants in the air based on the pollutants’ size. Then the samples were analyzed in the laboratory.

Air collected on the Red Line had more particulate matter — tiny, toxic, airborne particles — than either the air from the Gold Line or around USC, the scientists reported online in the journal Environmental Science and Technology on July 5.

The air collected by Red Line travelers had more than twice as many coarse particles — ones greater than 2.5 micrometers in diameter — than the air around USC or in the Gold Line trains. Coarse particles are typically found near roads or dusty industries, and the authors think that being inside the train may have protected commuters from exposure to them.

The Red Line air also had about 70% more fine particles than found on the Gold Line and at the USC site. Fine particles are smaller than 2.5 micrometers in diameter and can be emitted directly when fuel burns; they also form when gases from power plants or cars react with sunlight and water vapor in the air.

According to the Environmental Protection Agency, the smaller the particles are, the more dangerous they are -- because they can penetrate deeper into the lungs. Once inside the body, they can cause heart and lung damage.

In a news release, Constantinos Sioutas, an engineer at USC and the first author of the study, said that the Red Line’s air is still much cleaner than what commuters encounter on L.A. freeways. Though freeway air wasn’t measured in this study, he said his team has conducted several other experiments over the last 10 years showing that the concentrations of pollutants on highways around Los Angeles can be five to 10 times higher than in your average urban neighborhood.


The take-home message: Riding the train not only helps the environment, it could help keep you healthier in the long run.

Here’s a link to the study. (Unfortunately, you’ll have to cough up money if you want to read more than the abstract.)