Ambient Measurements of Heterogeneous Ozone Oxidation Rates of Oleic, Elaidic, and Linoleic Acid Using a Relative Rate Constant Approach in an Urban Environment

Abstract Long‐chain unsaturated fatty acids (uFAs), such as oleic acid, undergo rapid degradation via heterogeneous reactions with atmospheric oxidants upon emission. The oxidation mechanism and kinetics have been extensively studied in laboratory experiments. However, quantitative knowledge of degradation rates under real‐world atmospheric conditions is scarce. We obtained the nighttime decay rates of three cooking‐related uFAs using a relative rate approach applied to bihourly measured data in urban Shanghai. The estimated lifetime of oleic acid was 6 h under conditions of ∼12 ppb ozone and 60%–100% relative humidity encountered at our urban location or an inferred ∼2 h at a higher ozone level of ∼40 ppb. The decay rates of elaidic and linoleic acid are determined to be 0.62 and 1.37 that of oleic acid, respectively. This work provides the first kinetic data pertaining to real‐world conditions. They are valuable for constraining the modeling of heterogeneous aging of ambient organic aerosols.