Prolonged Atmospheric Chemical Lifetime of Unsaturated Fatty Acids From Cooking Sources Observed in Beijing During Wintertime

Chemical aging of organic aerosol (OA) is an important process for determining its environmental impacts. Previous laboratory and modeling studies have suggested that chemical aging of OA slows at lower temperatures due to increased particle viscosity, which hampers the diffusion of oxidants within the particle phase. However, evidence from field measurements has been lacking. For tackling the issue, we conducted atmospheric measurements of the molecular‐level chemical composition of OA using an online instrument in Beijing during wintertime. Unsaturated fatty acids from cooking such as oleic acid were detected. Apparent second‐order reaction rate constants ( k 2 ) of oleic acid with O 3 were retrieved from the data, especially focusing on oleic acid emitted during dinnertime. The k 2 values measured at cold winter nights in Beijing were found to be lower by an order of magnitude than those observed from residential cooking experiments at room temperature. The difference is quantitatively consistent with the temperature dependence of k 2 for simulated cooking aerosol in previous laboratory studies. This result suggests that the chemical aging of ambient OA is influenced by temperature‐induced changes in viscosity, underscoring the need to account for temperature effects when estimating the fate of OA across the broad atmospheric temperature range.