Heterogeneity in urban air quality impacts inferred from ground-based monitoring networks during the COVID-19 pandemic

Abstract:

The COVID-19 pandemic resulted in mass shutdowns in cities and countries around the world that led to significant decreases in traffic, industrial, and social activities. Previous work based on satellite data have shown an overall decrease in air pollution. In this work, the ten largest metropolitan statistical areas in the United States were analyzed to determine the effect of the pandemic on the urban air pollutant burden with PM2.5 mass concentrations being the primary pollutant of interest. We investigated changes in air pollutant concentrations for the entire duration of the shutdown (4-10 weeks) as well as the same length of time which preceded the shutdown for both 2019 and 2020. Data from 2019 were compared to that of 2020 for both the pre-shutdown (PS) and during-shutdown (DS) periods. Mobility data show a maximum decrease in socioeconomic activity within the first two weeks of the shutdown, therefore a shorter, two-week period was also studied to capture the largest effect of the shutdowns. The full shutdown period and the two-week period displayed differing changes in PM2.5 for the inter-year and intra-year comparisons when compared with the data from a time with normal activity. The full period was on average consistent between PS and DS periods, however the two week period had an average decrease of 20% for both inter-year and intra-year comparisons. The drop in PM2.5 was found to be inversely proportional to population density. However, this trend was not consistent across all cities studied. For example, Dallas and Houston had an increase in PM2.5 during the shutdown period for both the full and two-week periods, unlike New York and Chicago which had decreases, making an overall pandemic impact difficult to interpret. Ongoing analysis is focused on exploring reductions in other pollutants (e.g., NO2 and CO) and extending the analysis to other cities. The analysis will also be expanded to include data from 2015 to 2019. The data from these pre-COVID years will be averaged to create a more reliable baseline for concentrations during normal levels of activity. Our work will help in understanding the overall effect of COVID-19 pandemic on the air quality in the United States.