Otay-Mesa, San Diego County, USA, is located adjacent to a major US-Mexico land Port of Entry (POE), which is the second busiest commercial POE along the US-Mexico border. Concerns about air pollution in Otay-Mesa from sources in Mexico prompted this analysis. Data on hourly fine particulate air pollution (PM2.5) was obtained from the Otay- Mesa monitor operated by the San Diego Air Pollution Control District (SDAPCD) at Donovan State Prison (DVN). Prisoners are considered a vulnerable population and disparities in air pollution levels are considered an environmental justice issue. This thesis examined hourly PM2.5 from 2/1/2015 through 12/31/2016. Wind and pollution roses were plotted using the R statistical program to examine seasonal and diurnal variation. To determine whether location near the border disproportionately affected pollution levels in near-border areas, 24-hour back trajectories were also plotted using HYSPLIT and R for days on which the daily average PM2.5 concentrations were more than the 95th percentile higher than the downtown San Diego SDAPCD monitor (31 days). ‘Control’ days were also selected. Overall, the mean PM2.5 concentration was 12.5 μg/m3, with the highest mean in June 2016 (17.1 μg/m3). The dominant wind direction overall was from the west and northwest, but PM2.5 concentrations were higher during wind directions from Mexico (from southeast and south-southeast, over 50% of hours exceeded 17 μg/m3, compared with 25% of northwestern and 18% of western winds), mostly at night. June exhibited a pattern of pollution from daytime westerly winds. Examination of back trajectories indicated that the dominant influence on differentially polluted ‘test’ days was from the North (Los Angeles and San Diego), rather than from Mexico, although there was some evidence that winds from Mexico might elevate pollution at the near border site during the winter months. In conclusion, this study provides data that elevated particulate pollution is associated with wind directions from south of the border. On days where pollution is higher at Otay-Mesa than at downtown San Diego, winds from the north are common. Further studies should be conducted to determine the sources on air quality in the border region.