Investigating ground-level ozone pollution in semi-arid and arid regions of Arizona using WRF-Chem v4.4 modeling

Ground-level ozone (O 3 ) pollution is a persistent environmental concern, even in regions that have made efforts to reduce emissions. This study focuses on the state of Arizona, which has experienced elevated O 3 concentrations over past decades and contains two non-attainment areas as designated by the U.S. Environmental Protection Agency. Using the Weather Research and Forecasting with Chemistry (WRF-Chem) model, we examine O 3 levels in the semi-arid and arid regions of Arizona. Our analysis focuses on the month of June between 2017 and 2021, a period characterized by high O 3 levels before the onset of the North American Monsoon (NAM). Our evaluation of the WRF-Chem model against surface Air Quality System (AQS) observations reveals that the model adeptly captures the diurnal variation of hourly O 3 levels and the episodes of O 3 exceedance through the maximum daily 8 h average (MDA8) O 3 concentrations. However, the model tends to overestimate surface NO 2 concentrations, particularly during nighttime hours. Among the three cities studied, Phoenix (PHX) and Tucson (TUS) exhibit a negative bias in both hourly and MDA8 O 3 levels, while Yuma demonstrates a relatively large positive bias. The simulated mean hourly and MDA8 O 3 concentrations in Phoenix are 44.6 and 64.7 parts per billion (ppb), respectively, compared to observed values of 47.5 and 65.7 ppb, resulting in mean negative biases of - 2.9 and - 1.0 ppb, respectively.Furthermore, the analysis of the simulated ratio of formaldehyde (HCHO) to NO 2 ( HCHO / NO 2 ; FNR), reveals interesting insights of the sensitivity of O 3 to its precursors. In Phoenix, the FNR varies from a VOC (volatile organic compound)-limited regime in the most populated areas to a transition between VOC-limited and NO x -limited regimes throughout the metro area, with an average FNR of 1.15. In conclusion, this study sheds light on the persistent challenge of ground-level O 3 pollution in semi-arid and arid regions, using the state of Arizona as a case study.

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Author Guo, Y.
Roychoudhury, C.
Mirrezaei, M. A.
Kumar, Rajesh
Sorooshian, A.
Arellano, A. F.
Publisher UCAR/NCAR - Library
Publication Date 2024-05-24T00:00:00
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Topic Category geoscientificInformation
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Metadata Date 2025-07-10T20:02:00.330268
Metadata Record Identifier edu.ucar.opensky::articles:27281
Metadata Language eng; USA
Suggested Citation Guo, Y., Roychoudhury, C., Mirrezaei, M. A., Kumar, Rajesh, Sorooshian, A., Arellano, A. F.. (2024). Investigating ground-level ozone pollution in semi-arid and arid regions of Arizona using WRF-Chem v4.4 modeling. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d77s7t0t. Accessed 02 August 2025.

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