High levels of air pollution, especially fine particulate matter (PM2.5). are a concern along the US-Mexico border. The Ports of Entry (POEs) at the San Diego-Tijuana interface bring traffic through local communities, in addition to long lines of idling vehicles waiting to cross the border. The San Ysidro POE (SYPOE) is the busiest passenger border crossing in the world, while the Otay Mesa POE is the second busiest commercial POE along the US-Mexico border, but routine governmental air pollution data is not collected at these locations. We utilized two low-cost monitors, the University of Washington (UW) Community Air Monitor and a commercial monitor (Edimax,Taipei, Taiwan), both of which transmitted real time pollution data over a cellular or Wi-Fi network. Hourly PM2.5 data was obtained from San Diego Air Pollution Control District at the Donovan site near Otay Mesa. We examined hourly PM2.5 from intermittent time periods between 2/1/2019 through 12/15/2019 from monitors located at the SYPOE, Otay Mesa POE and the La Mesa government air quality monitoring site in Tijuana. Forward trajectories of pollution originating at the Otay Mesa and SYPOE’s were plotted for all months in 2019 using the SplitR package for Rstudio® to determine locations near the border that could be disproportionately affected by PM2.5 from idling vehicles from the POEs. Overall, for months when comparisons between sites were available (April – September 2019), PM2.5 concentrations at the Otay Mesa POE (median, 25th-75th percentiles) were 47% greater than Donovan (16.6 μg/m3, 12.3-24.4 μg/m3 vs. 11.3 μg/m3, 8.0-15.8 μg/m3) and 38% greater than La Mesa (12.0 μg/m3, 9.3-16.0 μg/m3), with the highest median in July 2019 (19.0 μg/m3). PM2.5 concentrations at the SYPOE (13.3 μg/m3, 10.3-17.4 μg/m3) were 16% greater than Donovan and 9% greater than La Mesa, with the highest median in July 2019 (15.7 μg/m3). Forward trajectories indicate that the Otay Mesa and SYPOEs most heavily impact the US community of San Ysidro from December to February, and south and southeast Tijuana during the summer months. Reductions in the border wait times and reductions in commercial vehicle emissions, such as particle filters, would reduce community exposures in the region.