TROPOMI NO2 in the United States: A detailed look at the annual
averages, weekly cycles, effects of temperature, and correlation with
PM2.5
Abstract
Observing the spatial heterogeneities of NO2 air pollution is an
important first step in quantifying NOx emissions and exposures. This
study investigates the capabilities of the Tropospheric Monitoring
Instrument (TROPOMI) in observing the spatial and temporal patterns of
NO2 pollution in the Continental United States (CONUS). The high
instrument sensitivity can differentiate the fine-scale spatial
heterogeneities in urban areas, such as hotspots related to
airport/shipping operations and high traffic areas, and the relatively
small emission sources in rural areas, such as power plants and mining
operations. We also examine NO2 columns by day-of-the-week and find that
Saturday and Sunday concentrations are 16% and 24% lower respectively
than during weekdays. In cities with topographic features that inhibit
dispersion, such as Los Angeles, there appears to be a pollution
build-up from Monday through Friday, while cities which have better
dispersion have more variability during weekdays. We also analyze the
correlation of temperatures and NO2 column amounts and find that NO2 is
larger on the hottest days (>32C) as compared to warm days
(26C - 32C), which is in contrast to a general decrease in NO2 with
increasing temperature at lower temperature bins. Finally, we compare
column NO2 with estimates of surface PM2.5 and find fairly poor
correlation, suggesting that NO2 and PM2.5 are becoming increasingly
less correlated in CONUS. These new developments make TROPOMI NO2
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.