ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-8-7205-2008 Investigation of the hygroscopic properties of Ca(NO<sub>3</sub>)<sub>2</sub> and internally mixed Ca(NO<sub>3</sub>)<sub>2</sub>/CaCO<sub>3</sub> particles by micro-Raman spectrometry Liu Y. J. 1 Zhu T. 1 Zhao D. F. 1 Zhang Z. F. 1 State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environmental Science and Engineering, Peking University, Beijing 100871, China 09 12 2008 8 23 7205 7215 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/8/7205/2008/acp-8-7205-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/7205/2008/acp-8-7205-2008.pdf

To understand and predict the role of mineral aerosol particles processed by reactive nitrogen species in the atmosphere, the hygroscopic properties of both Ca(NO<sub>3</sub>)<sub>2</sub> and Ca(NO<sub>3</sub>)<sub>2</sub>-containing mineral particles must be well understood. Using a micro-Raman system, the hygroscopic behaviors of micro-sized individual Ca(NO<sub>3</sub>)<sub>2</sub> and internally mixed Ca(NO<sub>3</sub>)<sub>2</sub>/CaCO<sub>3</sub> particles in both dehumidifying and humidifying processes were investigated systematically. In addition to accurate quantification of the dependence of water content on relative humidity (RH), significant new spectroscopic evidence related to chemical structure was also obtained to confirm the occurrence of amorphous solid state and to better understand the phase transition process. The Ca(NO<sub>3</sub>)<sub>2</sub> particles exhibit reversible behavior in the dehumidifying and humidifying processes; they are in the state of solution droplets above 10% RH and amorphous hydrates below 7% RH, and phase transition occurs at 7–10% RH. The hygroscopic behavior of Ca(NO<sub>3</sub>)<sub>2</sub>/CaCO<sub>3</sub> particles is identical to that of pure Ca(NO<sub>3</sub>)<sub>2</sub> particles, suggesting a negligible effect of the slightly soluble CaCO<sub>3</sub> inclusion on the hygroscopic behavior of a(NO<sub>3</sub>)<sub>2</sub>/CaCO<sub>3</sub> particles.

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