Preprints
https://doi.org/10.5194/egusphere-2023-2844
https://doi.org/10.5194/egusphere-2023-2844
01 Dec 2023
 | 01 Dec 2023

An intercomparison of satellite, airborne, and ground-level observations with WRF-CAMx simulations of NO2 columns over Houston, TX during the September 2021 TRACER-AQ campaign

M. Omar Nawaz, Jeremiah Johnson, Greg Yarwood, Benjamin de Foy, Laura M. Judd, and Daniel L. Goldberg

Abstract. Nitrogen dioxide (NO2) is a precursor of ozone (O3) and fine particulate matter (PM2.5) – two pollutants that are above regulatory guidelines in many cities. Bringing urban areas into compliance of these regulatory standards motivates an understanding of the distribution and sources of NO2 through observations and simulations. The TRACER-AQ campaign, conducted in Houston, TX in September 2021, provided a unique opportunity to compare observed NO2 columns from ground-, airborne-, and satellite-based spectrometers. In this study, we investigate how these observational datasets compare, and simulate column NO2 using WRF-CAMx with fine resolution (444 x 444 m2) comparable to the airborne column measurements. We find that observations from the GEOCAPE Airborne Simulator (GCAS) instrument were strongly correlated (r2=0.80) to observations from Pandora spectrometers with a negligible bias (NMB=0.1 %). Remote-sensing observations from the TROPOMI instrument were generally well correlated with Pandora observations (r2=0.73) with a negative bias (NMB=-22.8 %). We intercompare different versions of TROPOMI data and find similar correlations across three versions but slightly different biases (from -22.8 % in v2.4.0 to -18.2 % in the NASA MINDS product). Compared to Pandora observations, the WRF-CAMx simulation had reduced correlation (r2=0.34) and a low bias (-25.5 %) over the entire study region. We find particularly poor agreement between simulated NO2 columns and GCAS-observed NO2 columns in downtown Houston an area of high population and roadway densities. These findings point to a potential underestimate of vehicle NOX emissions in the WRF-CAMx simulation driven by the Texas state inventory; and further investigation is recommended.

M. Omar Nawaz, Jeremiah Johnson, Greg Yarwood, Benjamin de Foy, Laura M. Judd, and Daniel L. Goldberg

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-2844', Steven Compernolle, 11 Dec 2023
  • RC1: 'Comment on egusphere-2023-2844', Anonymous Referee #1, 19 Dec 2023
  • RC2: 'Comment on egusphere-2023-2844', Anonymous Referee #2, 21 Dec 2023
M. Omar Nawaz, Jeremiah Johnson, Greg Yarwood, Benjamin de Foy, Laura M. Judd, and Daniel L. Goldberg
M. Omar Nawaz, Jeremiah Johnson, Greg Yarwood, Benjamin de Foy, Laura M. Judd, and Daniel L. Goldberg

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Short summary
NO2 is a gas with implications for air pollution. An air campaign conducted in Houston provided an opportunity to compare NO2 from different instruments and a model. Observations from aircrafts and the TROPOMI satellite instrument agreed well with measurements on the ground, however the latter estimated lower values. We find that NO2 simulated in our model performed worse and find the worst performance in downtown Houston, suggesting that vehicle emissions of NO2 may be underestimated.