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Evaluating and Improving Urban VOC Chemistry in Los Angeles using WRF-chem
Citation:
Schwantes, R., M. Coggon, B. McDonald, S. McKeen, J. He, H. Pye, R. Cohen, S. Zhang, A. Wilson, G. Gkatzelis, C. Warneke, J. Gillman, A. Lamplugh, J. Pieschl, I. Bourgeois, A. Rollins, E. Appel, R. Hornbrook, A. Hills, AND G. Frost. Evaluating and Improving Urban VOC Chemistry in Los Angeles using WRF-chem. AGU Fall Meeting, New Orlease, Louisiana, December 13 - 17, 2021.
Impact/Purpose:
Urban emissions are increasingly dominated by volatile chemical products. These emissions are more oxygenated than traditional vehicle emissions. Air quality model mechanisms developed for vehicle-dominated conditions need updates to accurately predict present-day air quality.
Description:
Presently, over half of the world’s population lives in urban regions and this fraction is expected to increase in the future. VOC mixtures in urban regions are changing as mobile emissions decline and emerging sources such as volatile chemical products (VCPs) and cooking emissions rise. Emissions from VCPs and cooking contain more oxygenated VOCs that are not well represented in traditional reduced chemical mechanisms like RACM_ESRL. This work begins with the RACM2_Berkeley2 mechanism, which is of the same family as RACM_ESRL, but updated to RACM2 and includes more complex biogenic VOC chemistry. RACM2_Berkeley2 is expanded to include more complex oxygenated VOC gas-phase chemistry (e.g., alcohols, glycols, and glycerol) important for VCP emissions to create the RACM2_Berkeley2_VCP mechanism. This added complexity will be useful to compare oxygenated VOCs more directly with observations and to ensure accurate representation of reactivity and oxidation chemistry. As a case study, this work uses WRF-chem to evaluate how well RACM_ESRL and RACM2_Berkeley2_VCP mechanisms simulate ozone, PANs, and general VOC chemistry in Los Angeles against the two FIREX-AQ transit flights and surface ozone monitors from AirNow during the summer of 2019. Insight gained from comparing and contrasting the predictive skill of these two different chemical mechanisms, will be presented to better understand the proper chemical mechanism complexity needed to accurately simulate urban ozone, PAN, and VOC chemistry.
