Air pollution poses a global public health risk. Exposure to fine particulate matter (PM2.5) air pollution is associated with adverse human health effects, including cardiovascular and respiratory effects. Air pollution is shown to disproportionately affect low-income and/or ethnic minority groups, and is considered an environmental justice issue. PM2.5 particulates from vehicle traffic, especially from diesel engines, contribute to high concentrations of PM2.5. The cities of El Cajon and Escondido in San Diego, California, are surrounded by mountainous terrain and are prone to inversion layers that trap air pollution. Interstates 15 and 8 also run through Escondido and El Cajon, respectively, and are heavily congested. To investigate whether these communities might be considered environmental justice communities, five years of air pollution data (2009-2013) were analyzed from the San Diego County Air Pollution Control District air-monitoring network. Data included PM2.5, CO, NO, NO2, wind speed and wind direction. The 5-year mean PM2.5 concentrations in the Escondido (13.3μg/m3) and El Cajon (13.6 μg/m3) sites were elevated compared to the Downtown (12.9 μg/m3), Alpine (11.4 μg/m3), and Camp Pendleton (10.8 μg/m3) sites. Concentrations CO, NO, and NO2 were highest during the hours of 0600-0800 and 1800-2000, especially during low wind speeds. The highest concentrations of PM2.5 occurred in December for Escondido (18.8 μg/m3) and El Cajon (18.1 μg/m3), with high concentrations overnight. Seasonal meteorology and traffic patterns likely contribute to elevated PM2.5 concentrations in Escondido and El Cajon measured at the SDAPCD monitoring sites. The findings of elevated PM2.5 levels, combined with the presence of vulnerable population at these locations, add to evidence that these areas should be considered environmental justice communities and should be considered for designation under California Assembly Bill 617. By identifying periods of high PM2.5 concentrations, residents and individuals responsible for vulnerable populations can potentially reduce outdoor exposure to PM2.5.