Christopher Lovett, Farimah Shirmohammadi, Mohammad H. Sowlat, Constantinos Sioutas 

Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, California 90089, USA

Received: September 22, 2017
Revised: November 2, 2017
Accepted: November 5, 2017
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Cite this article:
Lovett, C., Shirmohammadi, F., Sowlat, M.H. and Sioutas, C. (2018). Commuting in Los Angeles: Cancer and Non-cancer Health Risks of Roadway, Light-Rail and Subway Transit Routes. Aerosol Air Qual. Res. 18: 2363-2374.


  • Los Angeles commuters exposed to hazardous PM species face significant health risks.
  • PM species including PAHs, transition metals & EC present the greatest health risk.
  • Risk on the METRO red line subway is greater than light-rail or roadway exposures.
  • The METRO gold line light rail affords the least exposure & consequent health risk.


Workers within the megacity of Los Angeles are exposed to significant amounts of airborne particulate matter (PM) during their daily commutes, which often exceed 30–60 minutes each way. Chemical species present in roadway and railway PM, including Benzo[a]pyrene (BaP) and hexavalent chromium (Cr6+), present substantial cancer and non-cancer health risks. In the current study, PM samples were collected and quantitatively speciated along five major commuter routes, including the METRO red line (subway) and gold line (light rail), the I-110 and I-710 freeways, and high-density surface streets (Sunset and Wilshire Boulevards). Using these concentration data, along with cancer potency (CP) and Reference Dosage (RfD) factors obtained from the United States Environmental Protection Agency (USEPA) and California's Office of Environmental Health Hazard Assessment (OEHHA), cancer and non-cancer health risks were calculated. In contrast to previous research indicating that Polycyclic Aromatic Hydrocarbon (PAH) components of Los Angeles roadway PM (e.g., along the I-710 freeway) led to the greatest cancer risk, the current analysis reveals that exposure to carcinogenic transition metals, particularly hexavalent chromium, which are especially prevalent along the METRO red line, results in the greatest cancer and non-cancer health risks. Based on these data, the best option for commuters is to use above-ground light-rail transportation, which allows for reduced exposure to both traffic-generated PAHs and railway-related metals.

Keywords: Commuter health risk; On-road emissions; Subway; Particulate matter; Los Angeles


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