Heterogeneous photochemical aging of soot by NO_2 under simulated sunlight

摘要

The aging process of soot in the atmosphere can significantly influence its physical and chemical properties. Here, the heterogeneous photochemical aging of soot by NO_2 under simulated sunlight was investigated using in situ attenuated total internal reflection infrared spectroscopy. It was observed that simulated sunlight can enhance the aging process of soot by NO_2. The photochemistry of soot with NO_2 led to the formation of various nitro compounds and oxygen-containing species on the soot surface. The photolysis of the surface nitro compounds resulted in various carbonyl groups and gas-phase NO and HONO. The photochemical aging depended on the NO_2 concentrations and combustion conditions of soot production. The soot samples with high content of organic carbon (OC) showed high photochemical reactivity towards NO_2. This means that the active species mainly belong to OC components, which mainly consist of various polycyclic aromatic hydrocarbons (PAHs) and some unidentified components.