Changes in Air Quality in Los Angeles Associated with COVID-19 ?Safer-at-Home? Traffic Reductions

Reductions in ozone (O3) and particulate matter (PM) levels in California?s South Coast Air Basin (SoCAB) over the last decade have slowed for reasons that are not well understood. As restrictions were put in place to slow the spread of SARS-CoV-2 in SoCAB, substantial reductions in nitrogen oxide (NOx) and PM were observed?likely providing important new clues on the role of traffic emissions in the continuing air quality challenges in the Basin. The traffic reductions took place, however, within the context of precipitation at least three times the historical average. As the anomalously rainy period ended in the SoCAB, the levels of the secondary pollutant O3 returned to values comparable or exceeding those of previous years despite the sustained decrease in traffic flow. This project will analyze observations made during the dramatic reductions in traffic in spring and early summer 2020 (during the COVID-19 period) to better understand the factors contributing to poor air quality in the SoCAB. A hierarchy of analysis and modeling approaches will be used to study the 2020 data within the context of both previous observations and a repeat set of measurements proposed as part of the project for spring/summer 2022 when, presumably, traffic levels will be restored to normal. Together, the 2020 and 2022 data provide key observations that can inform what air quality management efforts will be most efficient to bring the Basin into attainment. In collaboration with other investigators in urban areas nationwide, the results from the study will also be synthesized to better inform air quality mitigation strategies in California and across the United States