Chemical Precursors to Wintertime Carbonyl and Ozone Formation

Abstract. Using the Framework for 0-D Atmospheric Modeling (F0AM), a zero-dimensional box model designed for simulating atmospheric chemistry, we simulated winter 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 purpose was to (1) identify key carbonyl precursors that act as important precursors to winter O₃ formation and determine how they form, (2) determine the extent to which carbonyl compounds were primarily or secondarily produced, (3) assess O₃ production potential, and (4) analyze how different hydrocarbon groups influence both carbonyl and O₃ formation. 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, respectively, to the O₃ production rate. SAPRC07 and RACM2 showed similar trends, while CB6 emphasized the generic group “ketones” as key contributors. 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.