Preprints
https://doi.org/10.5194/egusphere-2025-23
https://doi.org/10.5194/egusphere-2025-23
21 Jan 2025
 | 21 Jan 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Incorporation of multi-phase halogen chemistry into Community Multiscale Air Quality (CMAQ) model

Kiyeon Kim, Chul Han Song, Kyung Man Han, Greg Yarwood, Ross Beardsley, and Saewung Kim

Abstract. Recent studies have revealed that halogen radicals (Cl, Br, and I) significantly influence atmospheric oxidation capacity, affecting O3 formation or destruction. However, understanding of halogen chemistries remains limited. To better investigate atmospheric halogen chemistries, we incorporated halogen processes into the Community Multi-scale Air Quality (CMAQ) model: (i) emissions of Cl2, HCl, Br2, and HBr from anthropogenic sources, and Br2, I2, HOI, and halocarbons from natural sources; and (ii) 177 multi-phase halogen reactions. After developing the model, we examined its performance against observed data. The results demonstrated significant improvements in simulating observed nitryl chloride (ClNO2) mixing ratios at supersites. The index of agreement (IOA) improved from 0.41 to 0.66, and the mean bias (MB) decreased from -159.36 ppt to -25.07 ppt. These improvements were driven by four atmospheric key reactions: (i) ClO + ClO → Cl2; (ii) HOBr + Cl- → BrCl; (iii) different parameterization of γN2O5; and (iv) 2NO2 + Cl- → ClNO + NO3-. We then examined the net Ox production rate (P(Ox)), which increased from 3.08 ppb/h to 3.33 ppb/h on land and decreased from 0.21 ppb/h to 0.07 ppb/h over ocean in the presence of halogen radicals. Further analysis of the impacts of halogen processes on key atmospheric species revealed that levels of OH, HCHO, and NOx increased by ~0.007 ppt (5.5 %), ~0.03 ppb (1.6 %), and ~0.29 ppb (2.9 %), respectively, while levels of HO2 and VOCs decreased by ~0.45 ppt (5.3 %) and ~0.71 ppb (5.9 %), respectively.

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Kiyeon Kim, Chul Han Song, Kyung Man Han, Greg Yarwood, Ross Beardsley, and Saewung Kim

Status: open (until 10 Mar 2025)

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Kiyeon Kim, Chul Han Song, Kyung Man Han, Greg Yarwood, Ross Beardsley, and Saewung Kim
Kiyeon Kim, Chul Han Song, Kyung Man Han, Greg Yarwood, Ross Beardsley, and Saewung Kim

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Short summary
Despite the crucial role of halogen radicals in the atmosphere, the current CMAQ model does not account for multi-phase halogen processes. To address this issue, we incorporated 177 halogen reactions, together with anthropogenic and natural halogen emissions into the CMAQ model. Our findings reveal that incorporation of these halogen processes significantly improves model performances compared to ground observations. In addition, we emphasize the influence of halogen radicals on air quality.
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