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Description
In March 2020, the COVID-19 pandemic led to the reduction of human activities to attenuate its spread. The US government restricted travel across the US-Mexico border, including the Port of Entry at San Ysidro, CA (SYPOE); the busiest land border crossing in the Western Hemisphere. Nearby communities have concerns about air pollution caused by long lines of idling vehicles waiting at the SYPOE. This study examines black carbon (BC) and fine particulate matter (PM2.5) before (March 2019-March 2020) and during (March 2020-March 2021) COVID-19 US-Mexico border crossing restrictions, using data from a nearby government monitor and low-cost sensors deployed near the SYPOE, funded by an award to Casa Familiar, a community organization, from AB617. Hourly border wait times and open lanes posted in real time on the U.S. Customs and Border Protection website were archived by the University of Washington and multiplied to create a new variable proxy for vehicle emissions, BWTxL. Overall, significant decreases were observed for monthly BWTxL (-12 to -33%) during the ban. Despite BWTxL reductions, wait times up to 6 hours were experienced by northbound passengers during COVID-19 restrictions. PM2.5 generally decreased during the ban, while BC generally increased, up to 50% higher in November and December 2020 compared to a year earlier. Hourly BC and PM2.5 were highly correlated (ρ =.7, p<0.001) but were not highly correlated with BWTxL. These findings suggest that sources of air pollution during the travel ban may be generated by sources other than idling vehicles. Increased northbound wait times during the COVID-19 border restriction indicate the unequal burdens experienced by cross-border commuters. This project can inform future policies to mitigate border wait times and promote pollutant attribution assessments to improve air quality within the San Ysidro-Tijuana area. Keywords: air pollution, environmental justice, low-cost air monitoring, pandemic, international border
