The photoenhanced aging process of soot by the heterogeneous ozonization reaction†
The atmospheric aging of soot can significantly modify its composition and microstructure, likely leading to changes in its effects on climate and health. The photochemical aging process of soot by O3 under simulated sunlight was investigated using in situ attenuated total internal reflection infrared spectroscopy. Simulated sunlight could markedly enhance the aging of soot by O3, which produced various oxygen containing species such as lactones, anhydrides, ketones and aldehydes. Elemental carbon (EC) showed minor reactivity toward O3. The organic carbon (OC), which was mainly composed of various polycyclic aromatic hydrocarbons (PAHs) and some unidentified components, played a key role in the photochemical aging of soot by O3. The kinetics of aromatic species on soot can be well described by a pseudo-first order reaction. The fitting results of the pseudo first-order rate constant (k1,obs) as a function of O3 concentration demonstrated that the photochemical reaction of soot with O3 followed the Langmuir–Hinshelwood mechanism.