In situ DRIFTS study of hygroscopic behavior of mineral aerosol

In situ diffusion reflectance infrared Fourier transform spectroscopy was used to study the water adsorption on mineral oxides (SiO_2, α-Al_2O_3, MgO, Fe_2O_3, TiO_2). The results showed that all the water adsorption isotherms were well fitted with the Brunauer-Emmett-Teller (BET)- Ⅲ type equation, with the calculated monolayers occurring at 24%-30% relative humidity. It showed that about 1-5 layers of water adsorbed on oxides surfaces in ambient relative humidity (20%-90%). The measured deliquescence relative humidity of NaCl was (74±1)%, which demonstrated that DRIFTS is a useful method for the study the hygroscopic behavior of mineral dust. In addition, the limits of DRIFTS were also discussed.