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EPA, San Diego County Air District monitoring PM2.5 at San Ysidro border crossing

The US EPA and San Diego County Air Pollution Control District (SDAPCD), in cooperation with US Customs and Border Protection and the US General Services Administration have installed a new air pollution monitor at the San Ysidro Port of Entry. The US-Mexico San Ysidro border crossing is the busiest land port of entry in the Western Hemisphere; on average, 50,000 cars and buses and 25,000 pedestrians cross the San Ysidro port of entry daily.

The monitor measures PM2.5 (fine particulate matter up to 2.5 microns in diameter) in the form of soot from engine emissions, which can result in negative health effects when inhaled.

EPA provided $110,000 to the SDAPCD for the purchase, installation, and operation of the San Ysidro PM 2.5 monitor.

A 2014 study by researchers from the University of Washington and San Diego State University, published in the journal Atmospheric Environment, found that subject pedestrians who crossed the border at San Ysidro in pedestrian lanes had a 6-fold increase in exposure to 1-nitropyrene (1-NP, a marker for diesel exhaust), a 3-fold increase in exposure to CO, and a 2-fold increase in exposure to gravimetric PM2.5, vs. non-border commuters.


  • V.E. Galaviz, M.G. Yost, C.D. Simpson, J.E. Camp, M.H. Paulsen, J.P. Elder, L. Hoffman, D. Flores, P.J.E. Quintana (2014) “Traffic pollutant exposures experienced by pedestrians waiting to enter the U.S. at a major U.S.-Mexico border crossing,” Atmospheric Environment doi: 10.1016/j.atmosenv.2013.12.042

  • Penelope J.E. Quintana, Jill J. Dumbauld, Lynelle Garnica, M. Zohir Chowdhury, José Velascosoltero, Arturo Mota-Raigoza, David Flores, Edgar Rodríguez, Nicolas Panagon, Jamison Gamble, Travis Irby, Cuong Tran, John Elder, Vanessa E. Galaviz, Lisa Hoffman, Miguel Zavala, Luisa T. Molina (2014) “Traffic-related air pollution in the community of San Ysidro, CA, in relation to northbound vehicle wait times at the US–Mexico border Port of Entry,” Atmospheric Environment doi: 10.1016/j.atmosenv.2014.01.009


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