Logo: University of Southern California

Viterbi School Researcher Analyzes Breaths of (Not So) Fresh Air

All Los Angeles commuters - on subway, light rail, and cars - are exposed to high levels of particulate pollution, new study finds
Robert Perkins
November 01, 2011 —

Commuters on the Los Angeles Red Line subway are exposed to higher levels of potentially hazardous components of particulate matter in the air - in some cases twice as much - as commuters on the above-ground Gold Line light rail, according to a new USC study.

However, the Metro system’s levels of these air pollutants, some of which are known carcinogens, pale in comparison to the levels of particulate matter that bombard commuters stuck in traffic on the freeways.

click on the image to read a recent Los Angeles Times story on the research

Constantinos Sioutas, Fred Champion professor of civil and environmental engineering at the USC Viterbi School of Engineering, measured the concentrations and chemical composition of fine and coarse particles in the air while riding on the Red Line and the Gold Line of the Los Angeles Metro using small carry-on suitcases equipped with portable air samplers.

He also tested the air quality at USC to act as a control site that represents typical urban air quality levels in Los Angeles.

The amount of particulate matter in the air on the Gold Line was similar to that in the air at USC, while the amount measured on the Red Line significantly was higher. Sioutas attributed the additional particulate matter in large part to the dust produced by the braking of trains approaching stations in the enclosed environment of the subway.

Sioutas, who uses the Gold Line in his commute to work at USC, said that even the Red Line’s air is an order of magnitude cleaner than the air that commuters face on the freeways in Los Angeles.

“The air in the light rail system is quite typical of what we breathe in urban L.A. if not actually cleaner,” he said. “However, several studies by our group and others in the past decade have shown that the concentrations of deleterious particulate air pollutants inside freeways, to which millions of commuters are exposed daily in L.A., are anywhere from five to 10 times higher than an urban site.

“This makes the exposure levels in the light rail and even the subways lines much, much lower than those inside freeways and busy arterial routes,” Sioutas explained.

His findings were published online by Environmental Science & Technology.

The American Lung Association likens the damaging effects of particle pollution damages to those of cigarette smoking, linking it to respiratory and cardiovascular illness, among other things.

“It’s really an array of health effects,” Sioutas said. For that reason, though Sioutas is a supporter of public transportation in general, he said he believes the future lies in expanding the county’s rail system.“There’s no other way. Buses are not the answer as they contribute to both traffic congestion as well as to air pollution,” he said.

Sioutas’ upcoming research will focus on providing more accurate data on just how unhealthy those streets are by equipping moving cars with air quality sensors.

Until now, most measurements of street air quality have relied on sensors placed on the side of roads, which do not capture the full extent of pollution that commuters are subjected to, Sioutas said.

This research was funded by the METRANS Transportation Center.