Hygroscopicity measurement of sodium carbonate, β-alanine and internally mixed β-alanine/Na2CO3 particles by ATR-FTIR

Water-uptakes of pure sodium carbonate (Na2CO3), pure beta-alanine and internally mixed beta-alanine/Na2CO3 aerosol particles with different mole ratios are first monitored using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) technique. For pure Na2CO3 aerosol particles, combining the absorptions at 877 and 1422 cm(-1) with abrupt water loss shows the efflorescence relative humidity (ERH) of 62.9%-51.9%. Upon humidifying, solid Na2CO3 firstly absorbs water to from Na2CO3 center dot H2O crystal at 72.0% RH and then deliquesces at 84.5% RH (DRH). As for pure beta-alanine particles, the crystallization takes place in the range of 42.4%-33.2% RH and becomes droplets at similar to 88.2% RH. When beta-alanine is mixed with Na2CO3 at various mole ratios, it shows no efflorescence of Na2CO3 when beta-alanine to Na2CO3 mole ratio (OIR) is 2:1. For 1:1 and 1:2 beta-alanine/Na2CO3 aerosols, the ERHs of Na2CO3 are 51.8%-42.3% and 57.1%-42.3%, respectively. While beta-alanine crystal appears from 62.7% RH for 2:1 and 59.4% RH for both 1:1 and 1:2 particles and lasts to driest state. On hydration, the DRH is 44.7%-75.2% for Na2CO3 with the OIR of 1:1 and 44.7%-69.0% for 1:2 mixture, and those of beta-alanine are 74.8% for 2:1 mixture and 68.9% for two others. After the first dehumidification-humidification, all the water contents decrease despite of constituent fraction. And at similar to 92% RH, the remaining water contents are 92%, 89% and 82% at similar to 92% RH, corresponding to OIR of 2:1, 1:1 and 1:2 mixed system, respectively. (c) 2019 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.