Hygroscopicity of internally mixed particles glycine/NaNO3 studied by FTIR-ATR technique

Internal mixed aerosol particles in atmosphere often take the drastic physical property changes owing to interactions between compositions. Hygroscopicity and phase transition behavior of mixed particles composed of glycine and NaNO3 with different organic to inorganic molar ratios (OIRs) have been investigated by using Fourier transform infrared attenuated total reflection spectroscopy (ATR-FTIR). It is found that pure glycine particles effloresce when the relative humidity (RH) is similar to 64.5% and do not deliquesce on humidifying. The efflorescence and deliquescence point for pure NaNO3 particles are similar to 54% RH and similar to 91.9% RH, respectively. For the internal mixed glycine/NaNO3 particles, there exhibit various hygroscopicities and solid-aqueous phase transitions dependent upon the OIR. When the OIRs are 2: 1 and 1: 1, NaNO3 particles cannot crystallize. When the OIRs are 1: 2, 1: 4 and 1: 8, crystalline ratios are similar to 31%, similar to 45% and 72%, NaNO3 effloresce at similar to 44.7% RH, similar to 35.2% RH and similar to 35% RH, respectively. For all studied mixture particles, glycine can crystallize. For OIRs of 2:1, 1:1, 1:2, 1:4 and 1:8, the crystalline fractions of glycine are similar to 78%, 89%, 93%, 94% and 95%, respectively, corresponding to the ERH range of 74% - 42%, 73% - 35.9%, 65.5% - 19.2%, 35.2% - 8.1% and 35% - 3.8%. It shows that both NaNO3 and glycine crystals are favored by more enriched NaNO3. On hydration, the DRHs of NaNO3 for mixtures with OIR of 1: 2, 1: 4 and 1: 8 are similar to 87.4%, similar to 87% and 85.4%, respectively. Glycine in mixtures deliquesces at similar to 99% (incomplete deliquescence), similar to 98.3%, similar to 97.3%, similar to 93.3%, similar to 85.4% RH, respectively, with decreasing OIR. The results suggest the positive effect of NaNO3 on the deliquescence of glycine and NaNO3.