Local scale air quality impacts in the Los Angeles Basin from increased port activity during 2021 supply chain disruptions

Increased throughput and container ship backlogs at the Ports of Los Angeles and Long Beach due to supply chain disruptions related to the Covid-19 pandemic caused a significant increase in the number of ships near the California coast, leading to concerns about increased air pollution exposure of nearby communities. We use a combination of satellite-based observations from TROPOMI and ground-based observations from routine surface monitoring sites with chemical transport model results to analyze the changes in NO2 and PM2.5 in the Los Angeles Basin during a period in 2021 when the number of ships was at its peak. Using simulations to account for meteorological effects, changes are apportioned to emissions and meteorology. The largest emission-related changes in column NO2 occurred immediately east of the ports where emission-related NO2 increased by 28% compared to the baseline (2018-2019 average). In Central Los Angeles emission reductions led to a 10% decrease in NO2 during the same period. Emission-related PM2.5 increased by 0.7 µg/m3 on average with a maximum increase of 4.5 µg/m3. The emission/meteorology attribution method presented here provides a way to infer emission-influenced changes in air quality that are consistent with observations and suggests that both NO2 and PM2.5 were elevated in parts of the Los Angeles area during a period of increased port activity.