Reduced Air Pollution Disparity between EJ and non-EJ communities in California during the COVID-19 Pandemic: Lessons Learned for Emission Mitigation Strategies

Abstract:

California experienced significant reduction in human activities following the Governor’s Executive Order N-33-20 (i.e., shelter-in-place order) in response to the COVID-19 pandemic. As a result, anthropogenic emissions of multiple air pollutants, such as nitrogen dioxide (NO₂), decreased substantially in the State. The NO₂ levels are able to effectively indicate the spatiotemporal variations of combustion source emissions (e.g., traffic) due to its relatively short lifetime. Since NO₂ is a regulated pollutant, such reductions in anthropogenic emissions provided a natural experiment that enabled us to understand the future impact of continued NO₂ mitigation strategies on exposure and health disparities between various communities in California.

This study examined the changes in satellite TROPOspheric Monitoring Instrument (TROPOMI) tropospheric NO₂ levels between socially disadvantaged (Environmental Justice; EJ) communities, defined by CalEnviroScreen 3.0, and all other (non-EJ) communities in California during the COVID-19 pandemic. Across California, the NO₂ levels decreased in EJ and non-EJ communities by 35.5% and 21.5%, respectively, from February 20 – March 4, 2020 (i.e., before shelter-in-place order) to April 2 – 15, 2020 (i.e., after shelter-in-place order; a period of the lowest vehicle miles traveled (VMT) and the highest social distancing (IHME’s mobility data)). Although TROPOMI NO₂ levels were consistently higher in the EJ communities than the non-EJ communities throughout the study period, the NO₂ disparity decreased from 56.4% (i.e., 56.4% higher NO₂ in EJ communities) before shelter-in-place order down to 24.0% in mid-April. The disparity started to increase thereafter as VMT began returning to the levels before the shelter-in-place order. This result demonstrated that emission control and VMT reduction of on-road mobile sources can significantly reduce the existing air quality disparity between EJ and non-EJ communities.