Simulated Surface‐Column NO 2 Connections for Satellite Applications

Observations of near‐surface NO 2 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 NO 2 VCD is sensitive to column calculation technique. With hourly daytime satellite‐based NO 2 observations newly available from the TEMPO instrument, the timing and magnitude of cycles in near‐surface NO 2 versus column NO 2 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. Nitrogen dioxide (NO 2 ) is a major air pollutant that may be measured from the ground or from satellites in space. Over the U.S., hourly satellite data are now available from a new instrument called TEMPO. We use a computer model to understand the expected relationship between the satellite column and ground‐level measurements. We find that the connection between the surface and column varies across the day: TEMPO observations are more likely to see morning peak and daytime minimum near‐surface amounts; TEMPO observations may miss evening peak near‐surface amounts. By helping to connect space‐based data with on the ground air quality, this work will help inform the timing of surface‐column connections to better interpret new hourly satellite observations for health and air quality applications. Satellite observations of nitrogen dioxide (NO 2 ) show column values, which show different hourly patterns than surface monitoring of NO 2 Column NO 2 values lag surface NO 2 in the morning but lead surface NO 2 in the evening Model simulations of column NO 2 are sensitive to calculation approach