Hydrocarbon and carbonyl contributions to wintertime ozone formation in the Uinta Basin, Utah

Abstract. Using the Framework for 0-D Atmospheric Modeling (F0AM), a zero-dimensional box model designed for simulating atmospheric chemistry, we simulated winter ozone (O3) formation in the Uinta Basin, Utah, with four chemical mechanisms: the Master Chemical Mechanism (MCMv331), Statewide Air Pollution Research Centre Mechanism (SAPRC07), Regional Atmospheric Chemistry Mechanism (RACM2), and Carbon Bond Mechanism (CB6). Our aim was to investigate the chemical processes linking hydrocarbon emissions to the formation of O3 in winter, with a focus on the role of carbonyls as O3 precursors, their primary versus secondary origins, and the impact of various hydrocarbon groups on carbonyl and O3 production across four chemical mechanisms. Regarding carbonyl origins, the final emission flux for carbonyls was near zero, indicating that they were mostly secondary photochemical products. MCMv331 identified formaldehyde and acetaldehyde as the dominant O3 precursors, contributing 0.20 and 0.06 ppb h−1, respectively, to the O3 production rate. Similarly, SAPRC07 and RACM2 identified formaldehyde and acetaldehyde as the dominant carbonyl contributors to O3 production, while CB6 emphasized the generic group “ketones” as key contributors due to its lumping of higher molecular weight carbonyls into a single species. Across all mechanisms, alkanes were the most influential precursor group for the formation of carbonyls and O3. Including heterogeneous chemistry in the model resulted in a modest (1 ppb) decrease in O3 levels without altering the relative importance of precursors. This study highlights the importance of primarily emitted organic groups in winter O3 production and provides insights into O3 reduction strategies in the Uinta Basin and similar regions.