The formation and growth of calcium sulfate crystals through oxidation of SO2 by O3 on size-resolved calcium carbonate |
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| Authors: | Ying Zhang Shengrui Tong Maofa Ge Bo Jing Siqi Hou Fang Tan Yi Chen Yucong Guo Lingyan Wu |
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| Affiliation: | State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 P. R. China.; University of Chinese Academy of Sciences, Beijing 100049 P. R. China ; CAS Research/Education Center for Excellence in Molecular Sciences, Beijing 100190 P. R. China ; State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081 P. R. China |
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| Abstract: | Calcium sulfate is a major constituent of atmospheric sulfate, with a typical rod-like morphology ranging from several hundred nanometers to approximately two micrometers observed in field studies. However, the chemical formation mechanism is still not well known. In this study, the kinetics and mechanism for the formation and growth of rod-like calcium sulfate crystals through oxidation of SO2 by O3 on size-resolved CaCO3 at different relative humidity (RH) were investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and scanning electron microscopy (SEM). We found that the concentration and formation rate of sulfate decreased with the increasing diameter of CaCO3 particles, and thus smaller particles could enhance the formation of sulfate due to more reactive sites on smaller particles. The rod-like calcium sulfate crystals were formed only at RH above 60% and in the presence of reactant gases through the heterogeneous pathway. The liquid-like water layer formed by promotion of high RH in the presence of reactant gases could facilitate the formation and aggregation of calcium sulfate hydrates and thus promote the formation and growth of rod-like calcium sulfate crystals. This study provides a possible mechanism for the formation and growth of rod-like calcium sulfate crystals existing in the atmosphere.The heterogeneous formation pathway of rod-like calcium sulfate crystals in the atmosphere. |
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