Al-Hosney H A, Grassian V H
Department of Chemistry, University of Iowa, Iowa City 52242, USA.
Phys Chem Chem Phys. 2005 Mar 21;7(6):1266-76. doi: 10.1039/b417872f.
Calcium carbonate (CaCO3) is a reactive component of mineral dust aerosol as well as buildings, statues and monuments. In this study, attenuated total reflection (ATR) and transmission Fourier transform infrared spectroscopy (FTIR) have been used to study the uptake of water, sulfur dioxide and nitric acid on CaCO3 particles at 296 K. Under atmospheric conditions, CaCO3 particles are terminated by a Ca(OH)(CO3H) surface layer. In the presence of water vapor between 5 and 95% relative humidity (RH), water molecularly adsorbs on the Ca(OH)(CO3H) surface resulting in the formation of an adsorbed thin water film. The adsorbed water film assists in the enhanced uptake of sulfur dioxide and nitric acid on CaCO3 in several ways. Under dry conditions (near 0% RH), sulfur dioxide and nitric acid react with the Ca(OH)(CO3H) surface to form adsorbed carbonic acid (H2CO3) along with sulfite and nitrate, respectively. Adsorbed carbonic acid is stable on the surface under vacuum conditions. Once the surface saturates with a carbonic acid capping layer, there is no additional uptake of gas-phase sulfur dioxide and nitric acid. However, upon adsorption of water, carbonic acid dissociates to form gaseous carbon dioxide and there is further uptake of sulfur dioxide and nitric acid. In addition, adsorbed water increases the mobility of the ions at the surface and enhances uptake of SO2 and HNO3. In the presence of adsorbed water, CaSO3 forms islands of a crystalline hydrate whereas Ca(NO3)2 forms a deliquescent layer or micropuddles. Thus adsorbed water plays an important and multi-faceted role in the uptake of pollutant gases on CaCO3.
碳酸钙（CaCO₃）是矿物粉尘气溶胶以及建筑物、雕像和古迹的一种活性成分。在本研究中，衰减全反射（ATR）和透射傅里叶变换红外光谱（FTIR）已被用于研究在296K下碳酸钙颗粒对水、二氧化硫和硝酸的摄取。在大气条件下，碳酸钙颗粒表面由Ca(OH)(CO₃H)表面层终止。在相对湿度（RH）为5%至95%的水蒸气存在下，水分子吸附在Ca(OH)(CO₃H)表面，形成吸附的薄水膜。吸附的水膜通过多种方式协助增强碳酸钙对二氧化硫和硝酸的摄取。在干燥条件下（接近0%RH），二氧化硫和硝酸分别与Ca(OH)(CO₃H)表面反应，形成吸附的碳酸（H₂CO₃）以及亚硫酸盐和硝酸盐。在真空条件下，吸附的碳酸在表面上是稳定的。一旦表面被碳酸覆盖层饱和，气相中的二氧化硫和硝酸就不会有额外的摄取。然而，一旦吸附了水，碳酸就会解离形成气态二氧化碳，二氧化硫和硝酸会有进一步的摄取。此外，吸附的水增加了表面离子的迁移率，增强了对SO₂和HNO₃的摄取。在存在吸附水的情况下，CaSO₃形成结晶水合物岛，而Ca(NO₃)₂形成潮解层或微水坑。因此，吸附的水在碳酸钙对污染气体的摄取中起着重要且多方面的作用。
