Synergistic effect between SO2 and HCOOH on the surface of CaO

Abstract

Due to altering the properties of particles and the budget of trace gases, heterogeneous reactions on mineral aerosols become an important subject in the atmospheric chemistry. However, synergistic effects between trace gases on the surface of mineral aerosol are largely uncertain. In this work, the synergistic effect between SO2 and HCOOH on the surface of CaO was studied using in situ Diffusion Reflectance Infrared Fourier Spectroscopy (DRIFTS). From analysing of the spectral features and obtaining the kinetic curves, it is found that the heterogeneous reactions of SO2 and HCOOH on the surface of CaO blocked each other. In addtion, the formate and sulfite decreased when SO2 and HCOOH were introduced into the reaction chamber simultaneously. Synergistic effect between SO2 and HCOOH on the surface of CaO was mainly divided into two aspects according to step-by-step experiments. Less reactive sites available for adsorption because of the coexisting of SO2 inhibited the reaction of HCOOH on the surface of CaO, resulting in the decrease of the formation of formate. On the other hand, HCOOH could prevent SO2 from reacting with CaO so that the formation of sulfite decreased.