Concentrations and oxidative potential of fine particulate matter and black carbon inhalation doses at the major US-Mexico Port of Entry San Ysidro/El Chaparral

Abstract The San Ysidro/El Chaparral Land Port of Entry (SYPOE), located between San Diego, US and Tijuana, Mexico, is the busiest border crossing in the Western hemisphere, with long waiting times to all users. People crossing, working, or living near the SYPOE are exposed to vehicular pollutants, especially particles with aerodynamic diameters < 2.5 µm (PM2.5) and black carbon (BC), which have been linked to adverse health effects.This study presents the first PM2.5 and BC concentrations measurements made on the Mexican side of the SYPOE (2017 and 2019). The oxidative potential (OP) for PM2.5 and the inhalation dose of BC for various groups at the border were also evaluated. Autumn and winter show the highest PM2.5 concentrations at the SYPOE (mean 28.7 µg m− 3 and 28.2 µg m− 3, respectively). BC concentrations at the SYPOE were the highest in winter 2017 (mean 5.7 ± 6 µg m− 3), showing concentrations 2.3 times higher for periods with low wind speeds, compared to high winds. The highest OPDTT of PM2.5 was present in winter, with a value of 18.5 pmol min− 1 µg− 1 (0.6 nmol min− 1 m− 3). The highest average daily dose for pedestrians in autumn 2018 was 5.9 µg for a 60 min waiting time. For the workers, the highest average daily dose was in winter 2017 (19 µg for an average of a 10-hr work shift). Decreasing waiting times for pedestrians and adjusting work schedules for border workers on high concentrations days would reduce inhalation dose and improve environmental justice at the border.