Concentration and Oxidative Potential of Fine Particulate Matter at the Major US-Mexico Port of Entry San Ysidro/El Chaparral

RITA ZURITA, Penelope Quintana, Yanis Toledano-Magaña, Fernando Wakida, Lupita Montoya, Javier Castillo, Universidad Autónoma de Baja California, México

     Abstract Number: 475
     Working Group: Aerosol Exposure

Abstract
Epidemiological studies have reported adverse health effects of traffic-related air pollutants and roadway particulate matter (PM) has been shown to generate reactive oxygen species leading to oxidative stress. The dithiothreitol (DTT) assay is commonly used to determine the Oxidative Potential in PM (OP^DTT). 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. The objective of this study was to measure PM_2.5 concentrations and the associated OP^DTT from samples collected at the SYPOE. Black Carbon (BC) concentrations were also measured and the associated BC inhalation dose was estimated for pedestrians crossing the SYPOE.

Sampling took place in Tijuana, B.C., Mexico, about 200 m southeast of the SYPOE and from 2017 to 2019. PM_2.5 sampling was conducted following published Standard Operating Procedure MDL016. OP of PM_2.5 was determined using the DTT assay. BC concentrations were measured using a portable micro Aethalometer (Aeth Labs, AE51, California, US) and then used to estimate BC inhalation doses. Results showed that PM_2.5 concentrations exceeded the World Health Organization guideline (10 μg m^-3) about 64% of the sampling period. It was also determined that PM_2.5 and BC concentrations were higher during lower wind speeds. The OP^DTT was highest in winter, with a value of 18.5 pmol min^-1 µg^-1 (0.6 nmol min^-1 m^-3) and during longer waiting times. The highest BC inhalation dose estimated for pedestrians was in autumn (7.0 μg/ 60 min wait time). Decreasing the waiting time for vehicles to cross the border would impact the exposure and the inhalation dose of both workers and people crossing the border. Studies that evaluate the composition of PM_2.5 collected at such locations are necessary to better understand the negative effects they could have on the health of the affected populations.