Simulated Surface-Column NO2 Connections for Satellite Applications

Observations of near-surface NO₂ show a diurnal pattern with midday minima and daily maxima in the morning and evening. These surface cycles are dependent on chemical processing, transport, and emissions. We evaluate these cycles with the United States Environmental Protection Agency (EPA) community multiscale air quality (CMAQ) model data from the EPA Air Quality Time Series (EQUATES) project, compared with ground-based measurements from the EPA air quality system, two Pandora measurement sites, and satellite data from TROPOMI. We find that the morning vertical column density (VCD) lags surface concentrations by 1 hr on average, where this lag varies with location and day. The peak VCD can also lead the surface maximum concentration, especially in the evening, responding to transport and afternoon compression of the boundary layer. Modeled NO₂ VCD is sensitive to column calculation technique. With hourly daytime satellite-based NO₂ observations newly available from the TEMPO instrument, the timing and magnitude of cycles in near-surface NO₂ versus column NO₂ will help inform the utilization of hourly satellite data. This work will help inform the timing of surface-column connections to better interpret new hourly satellite observations for health and air quality applications, including emissions characterization.