FTIR-ATR Study On Hygroscopicity And Dynamics Of NaNO₃/glycerol Mixed Aerosols

Sodium nitrate, which is one of the components of aging sea salt aerosols, has attracted extensive attention of scientists. Even though the hygroscopic behaviors of NaNO3 had been extensively studied for many years, the hygroscopicity of NaNO3 aerosol is still ambiguous. Zhang et al. studied the nucleation rate of NaNO3 droplets in the efflorescence process in terms of microscopic kinetics view in 2014. This accounts for the difference of NaNO3 hygroscopicity results to a certain extent. In this thesis, we take the actual complex composition of aerosols into account and select the NaNO3/glycerol mixed aerosol droplets as the research object. By using the in situ FTIR-ATR technique, we observed the FTIR spectra changes of NaNO3/glycerol mixed aerosol droplets(OIR=0, 1:8, 1:4, 1:2, 1:1, 2:1) in the dehumidification process. And on the basis of FTIR spectra changes, the nucleation ratio and nucleation rate of NaNO3/glycerol mixed aerosol droplets(OIR=0, 1:8, 1:4, 1:2, 1:1, 2:1) was inferred.In the process of continuous decreasing of relative humidity(RH), NaNO3/glycerol aerosol droplets first reached the saturated state, which is a metastable state, and then the crystallization events occurred near the efflorescence relative humidity(ERH). First of all, it is found that the efflorescence RHs in mixed NaNO3/glycerol droplets is much lower and wider than that of NaNO3 droplets. The ERH of mixed NaNO3/glycerol droplets decreases with the increasing of OIR. For the NaNO3/glycerol droplets of OIR=2:1, the ERH even decreased to 15% RH. In addition, the nucleation rate of NaNO3 is slower and slower, and ratio of nucleation is smaller and smaller with the increasing of OIR.For the first time, we discussed the effect of glycerol on the NaNO3 nucleation rate. From the experiment results, we found that the addition of glycerol can affect the nucleation mechanism of NaNO3. For the NaNO3/glycerol droplets(OIR=1:8, 1:4, 1:2, 1:1), there appeared two nucleation mechanisms: heterogeneous nucleation at high supersaturation and homogeneous nucleation at low supersaturation. The results proved that glycerol makes the nucleation mechanism transfer from heterogeneous nucleation to homogeneous nucleation. In addition, the transformation became faster with the increasing OIR. In contrast, the NaNO3/glycerol droplets(OIR=2:1) experience the homogeneous completely.