Concentrations and Oxidative Potential of PM2.5 and Black Carbon Inhalation Doses at US–Mexico Port of Entry

Located between Mexico and the US, the San Ysidro/El Chaparral Land Port of Entry (SYPOE) is one of the busiest border crossings in the world. People with activities at the SYPOE are exposed to vehicular pollutants, especially particles with aerodynamic diameters < 2.5 µm (PM2.5) and black carbon (BC), both associated with adverse health effects. This study presents the first PM2.5 and BC concentration measurements collected on the Mexican side of the SYPOE. The oxidative potential (OP) for PM2.5 and the inhalation dose of BC for people at the border were also evaluated. Autumn and winter showed the highest PM2.5 concentrations (at 28.7 μg m−3 and 28.2 μg m−3, respectively). BC concentration peaked in the winter of 2017 (at 5.7 ± 6 μgm−3), demonstrating an increase during periods with low wind speeds. The highest OPDTT of PM2.5 was reached in winter, with a value of 18.5 pmol min−1 µg−1 (0.6 nmol min−1m−3). The highest average daily inhalation dose for pedestrians was registered in the autumn of 2018 (5.9 μg for a 60-min waiting time), whereas, for workers, it was in the winter of 2017 (19 μg for a 10-h shift on average). Decreasing waiting times for pedestrians and adjusting work schedules for border workers on high concentration days could ameliorate environmental justice.