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Water-uptakes of pure sodium carbonate (Na2CO3),pine β-alanine and intally mixed β-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.H2O crystal at 72.0％ RH and then deliquesces at 84.5％ RH (DRH).As for pure β-alanine particles,the crystallization takes place in the range of 42.4％-33.2％ RH and becomes droplets at ～88.2％ RH.When β-alanine is mixed with Na2CO3 at various mole ratios,it shows no efflorescence of Na2CO3 when β-alanine to Na2CO3 mole ratio (OIR) is 2∶1.For 1∶1 and 1∶2 β-alanine/Na2CO3 aerosols,the ERHs of Na2CO3 are 51.8％-42.3％ and 57.1％-42.3％,respectively.While β-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 β-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 ～92％ RH,the remaining water contents are 92％,89％ and 82％ at ～92％ RH,corresponding to OIR of 2∶1,1∶1 and 1∶2 mixed system,respectively.