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

Guo, Yafang; Roychoudhury, Chayan; Mirrezaei, Mohammad Amin; Kumar, Rajesh; Sorooshian, Armin; Arellano, Avelino F.

Ground-level ozone (Oinline-formula3) 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 Oinline-formula3 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 Oinline-formula3 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 Oinline-formula3 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 Oinline-formula3 levels and the episodes of Oinline-formula3 exceedance through the maximum daily 8 h average (MDA8) Oinline-formula3 concentrations. However, the model tends to overestimate surface NOinline-formula2 concentrations, particularly during nighttime hours. Among the three cities studied, Phoenix (PHX) and Tucson (TUS) exhibit a negative bias in both hourly and MDA8 Oinline-formula3 levels, while Yuma demonstrates a relatively large positive bias. The simulated mean hourly and MDA8 Oinline-formula3 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 inline-formula−2.9 and inline-formula−1.0 ppb, respectively.

Furthermore, the analysis of the simulated ratio of formaldehyde (HCHO) to NOinline-formula2 (inline-formula M15inlinescrollmathml chem normal HCHO / normal NO normal 2 61pt14ptsvg-formulamathimg51f0e9af560def289ad0c8cb437187a3 gmd-17-4331-2024-ie00001.svg61pt14ptgmd-17-4331-2024-ie00001.png ; FNR), reveals interesting insights of the sensitivity of Oinline-formula3 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 NOinline-formulax-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 Oinline-formula3 pollution in semi-arid and arid regions, using the state of Arizona as a case study.

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Guo, Yafang / Roychoudhury, Chayan / Mirrezaei, Mohammad Amin / et al: Investigating ground-level ozone pollution in semi-arid and arid regions of Arizona using WRF-Chem v4.4 modeling. 2024. Copernicus Publications.

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