TROPOMI NO ₂ in the United States: A Detailed Look at the Annual Averages, Weekly Cycles, Effects of Temperature, and Correlation With Surface NO ₂ Concentrations

Abstract

Observing the spatial heterogeneities of NO ₂ air pollution is an important first step in quantifying NO _X emissions and exposures. This study investigates the capabilities of the Tropospheric Monitoring Instrument (TROPOMI) in observing the spatial and temporal patterns of NO ₂ pollution in the continental United States. The unprecedented sensitivity of the sensor can differentiate the fine‐scale spatial heterogeneities in urban areas, such as emissions related to airport/shipping operations and high traffic, and the relatively small emission sources in rural areas, such as power plants and mining operations. We then examine NO ₂ columns by day‐of‐the‐week and find that Saturday and Sunday concentrations are 16% and 24% lower respectively, than during weekdays. We also analyze the correlation of daily maximum 2‐m temperatures and NO ₂ column amounts and find that NO ₂ is larger on the hottest days (>32°C) as compared to warm days (26°C–32°C), which is in contrast to a general decrease in NO ₂ with increasing temperature at moderate temperatures. Finally, we demonstrate that a linear regression fit of 2019 annual TROPOMI NO ₂ data to annual surface‐level concentrations yields relatively strong correlation ( R ² = 0.66). These new developments make TROPOMI NO ₂ satellite data advantageous for policymakers and public health officials, who request information at high spatial resolution and short timescales, in order to assess, devise, and evaluate regulations.

Key Points

• The high instrument sensitivity of Tropospheric Monitoring Instrument (TROPOMI) can measure NO ₂ pollution with unprecedented clarity compared to predecessor instruments

• We can now quantify pollution hotspots within cities such as those related to airport/shipping operations and high traffic areas

• Annual column NO ₂ observed by TROPOMI has good correlation ( R ² = 0.66) with EPA surface observations without any surface‐to‐column conversion