Carbonyl Compounds Regulate Atmospheric Oxidation Capacity and Particulate Sulfur Chemistry in the Coastal Atmosphere

Carbonyl compounds play a crucial role in the formation of ozone (O₃) and secondary aerosols, with recent studies particularly highlighting formaldehyde (HCHO) as a significant contributor to the missing particulate sulfur. However, evaluations based on field observations are limited, especially in clean marine environments. Utilizing observation data from a coastal mountain site in May 2021 in Qingdao, northern China, we reveal the important regulating effect of carbonyls in atmospheric oxidation capacity and particulate sulfur chemistry using detailed chemical box models. Photolysis of gaseous carbonyls accounted for >90% and >60% of the primary sources of HO₂ and RO₂, respectively, contributing 38% of net O₃ production. Notably, HCHO alone constituted 80% of the primary HO₂ and 15% of net O₃ production. Using a multiphase model with updated HCHO-related chemistry, we determine that HCHO chemistry can account for up to 30% of total particulate sulfur (the sum of hydroxymethanesulfonate and sulfate) and address more than one-third of the simulated sulfate gap. The emission-based multiphase model indicates that the HCHO-related pathway remains significant and can account for 20% of the particulate sulfur under clean marine conditions. These findings underscore the importance of carbonyls, particularly HCHO, in regulating the atmospheric oxidation capacity and particulate sulfur chemistry in the marine atmosphere, urging further laboratory studies on chemical kinetics and field measurements of particle-phase carbonyls.