Preprints
https://doi.org/10.5194/egusphere-2025-4664
https://doi.org/10.5194/egusphere-2025-4664
26 Sep 2025
 | 26 Sep 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

PAMS-Constrained Top-Down Calibration of VOC-Speciated CMAQ Simulations

Sheng-Po Chen, Chieh-Heng Wang, Yi-Yu Lee, Feng-Yi Cheng, and Jia-Lin Wang

Abstract. Accurate simulation of volatile organic compound (VOC) emissions and their role in ozone (O3) formation remains a persistent challenge in chemical transport models (CTMs). Most models rely on lumped surrogate species, limiting their ability to represent speciated VOCs and directly compare with observations. In this study, we develop an enhanced version of the Community Multiscale Air Quality model, termed CMAQ-PAMS, which explicitly incorporates 54 VOC species targeted by the Photochemical Assessment Monitoring Stations (PAMS) network in Taiwan.

We evaluate model performance during a representative high-ozone event in fall 2021 and apply a top-down calibration approach using hourly VOC data from 12 PAMS sites. The original simulation (OrigSIM) significantly misrepresents key species, largely due to reliance on U.S.-based speciation profiles. After adjustment, the modified simulation (ModSIM) shows substantial improvements in both individual species concentrations and group-level composition (e.g., alkanes, aromatics). Notably, acetylene, a key tracer of incomplete combustion, was underestimated in OrigSIM but successfully recovered in ModSIM.

Despite accounting for only ~32 % of total VOC emissions, PAMS species contribute up to 52 % of modeled domestic O3 formation, highlighting their disproportionate impact in VOC-limited regimes. Additionally, the CMAQ-PAMS framework enables the use of diagnostic ratios (e.g., propylene/acetylene) to identify emission sources and assess air mass aging. These findings underscore the importance of localized VOC profiling and demonstrate that the PAMS-constrained CMAQ-PAMS model provides a more chemically detailed and observationally anchored platform for ozone modeling and regulatory applications.

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Sheng-Po Chen, Chieh-Heng Wang, Yi-Yu Lee, Feng-Yi Cheng, and Jia-Lin Wang

Status: open (until 07 Nov 2025)

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Sheng-Po Chen, Chieh-Heng Wang, Yi-Yu Lee, Feng-Yi Cheng, and Jia-Lin Wang
Sheng-Po Chen, Chieh-Heng Wang, Yi-Yu Lee, Feng-Yi Cheng, and Jia-Lin Wang

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Short summary
Current chemical transport models often simplify chemical compounds, making it hard to match real-world observations. In this study, we enhanced a model to simulate 54 specific volatile organic compounds (VOCs) measured across Taiwan. By comparing with detailed monitoring data, we corrected emissions and improved predictions of VOCs. The results indicate that a small set of compounds has a significant impact on ozone, providing guidance for more effective air quality strategies.
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