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

The San Diego/Tijuana US-Mexico border crossing at the San Ysidro Port of Entry (POE) is the world's busiest international land border crossing (GSA, 2013). San Ysidro, California, is the US community immediately adjacent to the border crossing. More than 90% of San Ysidro residents are Hispanic, and the average household income is less than 60% of the San Diego regional average. This study investigated the San Ysidro POE as a source of traffic-related air pollutants in San Ysidro, especially in relation to wind direction and northbound vehicle wait times. The pollutants ultrafine particulate matter (UFP), black carbon (BC), and particulate matter <2.5 μm in diameter (PM2.5) were periodically sampled through the course of 2010 at four rooftop locations: one commercial establishment near the POE, two elementary schools in San Ysidro, and a coastal estuary reference site. Weather data from two nearby sites and northbound border wait times were also collected. Results indicate consistently higher daytime BC and UFP concentrations at the measurement sites near the POE. Pollution concentrations were higher during low wind speeds or when wind was blowing from the POE towards San Ysidro. In February, March and November measurements, black carbon pollution appeared to be significantly positively associated with the POE northbound wait times when the wind direction was blowing from the POE towards San Ysidro or during low wind speeds, but not when the wind direction was from the west/northwest towards the POE. This pilot study is the first to investigate the potential effect of the POE, especially the long northbound traffic delays, on the nearby community of San Ysidro. Disparities in traffic exposures are an environmental justice issue and this should be taken into account during planning and operation of POEs.