Examining the Summertime Ozone Formation Regime in Southeast Michigan Using MOOSE Ground‐Based HCHO/NO<sub>2</sub> Measurements and F0AM Box Model
Xiong Ying, Jiajue Chai, Huiting Mao, Noribeth Mariscal, Tara I. Yacovitch, B. M. Lerner, Francesca Majluf, Manjula R. Canagaratna, Eduardo P. Olaguer, Yaoxian Huang
Abstract
Abstract Ambient ozone (O 3 ) concentrations in Southeast Michigan (SEMI) can exceed the U.S. National Ambient Air Quality Standard. Despite past efforts to measure O 3 precursors and elucidate reaction mechanisms, changing emission patterns and atmospheric composition in SEMI warrant new measurements and updated mechanisms to understand the causes of observed O 3 exceedances. In this study, we examine the chemical drivers of O 3 exceedances in SEMI, based on the Phase I MOOSE (Michigan‐Ontario Ozone Source Experiment) field study performed during May to June 2021. A zero‐dimensional (0‐D) box model is constrained with measurement data of meteorology and trace gas concentrations. Box model sensitivity simulations suggest that the formaldehyde to nitrogen dioxide ratio (HCHO/NO 2 ) for the transition between the volatile organic compounds (VOCs)‐ and nitrogen oxides (NO x )‐limited O 3 production regimes is 3.0 ± 0.3 in SEMI. The midday (12:00–16:00) averaged HCHO/NO 2 ratio during the MOOSE Phase I study is 1.62 ± 1.03, suggesting that O 3 production in SEMI is limited by VOC emissions. This finding implies that imposing stricter regulations on VOC emissions should be prioritized for the SEMI O 3 nonattainment area. This study, through its use of ground‐based HCHO/NO 2 ratios and box modeling to assess O 3 ‐VOC‐NO x sensitivities, has significant implications for air quality policy and the design of effective O 3 pollution control strategies, especially in O 3 nonattainment areas.