Decreases in Near-Road NO and NO<sub>2</sub> Concentrations during the COVID-19 Pandemic in California
Jonathan Liu, Jonah Lipsitt, Michael Jerrett, Yifang Zhu
Abstract
The COVID-19 pandemic and resulting shelter-in-place measures led to widespread adoption of remote work policies and temporary business closures or operation curtailments, disrupting typical commuting patterns. This study investigates how these sudden shifts in traffic patterns affected near-road NO and NO2 concentrations in California. We used (1) near-road air pollution data from the U.S. Environmental Protection Agency’s AirNow database, (2) passenger and heavy-duty traffic data from the Caltrans Performance Monitoring System, and (3) weather data from MesoWest between January 1 and April 30 during the years 2017–2020 to model NO and NO2 concentrations as functions of highway traffic and meteorology. We then simulated NO and NO2 under business-as-usual traffic conditions and compared modeled data to observed values. Weekday passenger traffic significantly declined in Northern and Southern California by 29% and 24%, respectively. As a result, Northern and Southern California near-road locations experienced statistically significant declines in NO concentrations of 35% and 32% and in NO2 concentrations of 15% and 29%, respectively, compared to modeled estimates. As a natural experiment, our findings demonstrate that reduced vehicle activity significantly improved air quality, contributing to the body of evidence linking shelter-in-place measures and cleaner air.