Potential Errors in CMAQ NO:NO Ratios and Upper Tropospheric NO Impacting the Interpretation of TROPOMI Retrievals

Authors

Abiola S. Lawal, School of Civil & Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Drive, Atlanta, Georgia 30332-0355, United States.
T Nash Skipper, School of Civil & Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Drive, Atlanta, Georgia 30332-0355, United States.
Cesunica E. Ivey, Department of Civil and Environmental Engineering, 760 Davis Hall, University of California, Berkeley, California 94720-1710, United States.
Daniel L. Goldberg, Department of Environmental and Occupational Health, George Washington University, 950 New Hampshire Avenue NW, Washington, D.C. 20052, United States.
Jennifer Kaiser, School of Civil & Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Drive, Atlanta, Georgia 30332-0355, United States.
Armistead G. Russell, School of Civil & Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Drive, Atlanta, Georgia 30332-0355, United States.

Document Type

Journal Article

Publication Date

6-13-2025

Journal

ACS ES&T air

Volume

2

Issue

6

DOI

10.1021/acsestair.4c00198

Keywords

NO2 vertical column densities; NOx ratio; TROPOMI; chemical transport models; power plants; satellite retrievals

Abstract

Although Chemical Transport Models (CTMs) such as the Community Multiscale Air Quality Model (CMAQ) have been used in linking observations of trace gases to emissions and developing vertical column distributions, there remain consistent biases between CTM simulations and satellite retrievals. Simulated tropospheric NO vertical column densities (VCDs) are generally higher over areas with large NO sources when compared with retrievals, while an opposite bias is found over low NO regions. Artificial (i.e., numerical) dilution in the model, where emissions are mathematically dispersed uniformly within the originating CTM grid, can impact modeled NO:NO ratios, while lower CTM VCD levels often observed over rural areas can be attributed to missing emission sources of NO or flawed horizontal/vertical transport. Potential causes of both low and high biases are assessed in this study using CMAQ and Tropospheric Monitoring Instrument (TROPOMI) NO retrievals. It was found that more detailed modeling of NO plumes to assess the NO:NO ratio in two power plant plumes can mitigate the effect of artificial computational dilution, reducing the bias and overall differences in the observed vs modeled plumes (errors reduced by 30%). Adjustments of upper tropospheric NO led to overall improvements, with a reduction in CMAQ bias (-43% to -29%) and improved spatial correlation (0.81 to 0.86). This study highlights the importance of having accurate modeled NO:NO ratios when comparing models to retrievals and the impact of unintentional numerical dilution.

APA Citation

Lawal, Abiola S.; Skipper, T Nash; Ivey, Cesunica E.; Goldberg, Daniel L.; Kaiser, Jennifer; and Russell, Armistead G., "Potential Errors in CMAQ NO:NO Ratios and Upper Tropospheric NO Impacting the Interpretation of TROPOMI Retrievals" (2025). GW Authored Works. Paper 7415.
https://hsrc.himmelfarb.gwu.edu/gwhpubs/7415

Department

Environmental and Occupational Health