Multiphase Reaction of SO2 with NO2 on CaCO3 Particles. 1. Oxidation of SO2 by NO2

摘要

Heterogeneous/multiphase reaction of SO with NO on solid or aqueous particles is thought to be a potentially important source of sulfate in the atmosphere, for example, during heavily polluted episodes (haze), but the reaction mechanism and rate are uncertain. In this study, we investigated the heterogeneous/multiphase reaction of SO with NO on individual CaCO particles in N using Micro-Raman spectroscopy in order to assess the importance of the direct oxidation of SO by NO. In the SO/NO/HO/N gas mixture, the CaCO solid particle was first converted to the Ca(NO) droplet by the reaction with NO and the deliquescence of Ca(NO), and then NO oxidized SO in the Ca(NO) droplet forming CaSO, which appeared as needle-shaped crystals. Sulfate was mainly formed after the complete conversion of CaCO to Ca(NO), that is, during the multiphase oxidation of SO by NO. The precipitation of CaSO from the droplet solution promoted sulfate formation. The reactive uptake coefficient of SO for sulfate formation is on the order of 10, and RH enhanced the uptake coefficient. We estimate that the direct multiphase oxidation of SO by NO is not an important source of sulfate in the ambient atmosphere compared with the SO oxidation by OH in the gas phase.