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 (SiO2, α-Al2O3, MgO, Fe2O3, TiO2). 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.