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Disentangling the Impact of the COVID‐19 Lockdowns on Urban NO2 From Natural...

Goldberg, D. L., S. Anenberg, D. Griffin, C. A. McLinden, Z. Lu, and D. Streets (2020), Disentangling the Impact of the COVID‐19 Lockdowns on Urban NO2 From Natural Variability, Geophys. Res. Lett., 47, e2020GL089269, doi:10.1029/2020GL089269.

TROPOMI satellite data show substantial drops in nitrogen dioxide (NO2) during COVID‐19 physical distancing. To attribute NO2 changes to NOx emissions changes over short timescales, one must account for meteorology. We find that meteorological patterns were especially favorable for low NO2 in much of the United States in spring 2020, complicating comparisons with spring 2019. Meteorological variations between years can cause column NO2 differences of ~15% over monthly timescales. After accounting for solar angle and meteorological considerations, we calculate that NO2 drops ranged between 9.2% and 43.4% among 20 cities in North America, with a median of 21.6%. Of the studied cities, largest NO2 drops (>30%) were in San Jose, Los Angeles, and Toronto, and smallest drops (<12%) were in Miami, Minneapolis, and Dallas. These normalized NO2 changes can be used to highlight locations with greater activity changes and better understand the sources contributing to adverse air quality in each city. Plain Language Summary Nitrogen dioxide (NO2) is an air pollutant whose prevalence in urban areas is linked to fossil fuel combustion. The NO2 in our atmosphere is primarily a function of the magnitude of nitrogen oxide (NOx) emissions and weather factors such as sun angle, wind speed, and temperature. In this work, we developed two novel methods to account for weather impacts on daily pollution levels during COVID‐19 precautions. Once we accounted for favorable weather conditions that in some cases kept air pollution low independent of tailpipe emissions, calculated air pollutant emission reductions varied dramatically (9–43%) among 20 North American cities. Results can be used to understand factors contributing to inconsistent NO2 changes during physical distancing, which can inform the effectiveness of COVID‐19 protocols and aid future policy development. These methodologies will allow us to respond more quickly in future unintended experiments when emissions change suddenly.

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Applied Sciences Program (ASP)