Study On Kinetic Hygroscopic Properties Of Malonic Acid/Nitrate Aerosols By Vacuum FTIR

Atmospheric aerosols have great importance in affecting the climate change,air quality,atmospheric visibility and public health.The measurement of important physical and chemical parameters in the physical and chemical process of aerosols is of great significance in understanding the formation of atmospheric haze.In this study,we investigated the hygroscopicity,nucleation dynamics,molecular interactions and volatilization of gas generated by reactivity of malonic acid and its mixtures with nitrate aerosolsHerein,we utilized a novel approach based on a combination of a pulse relative humidity（RH）controlling system and a rapid scan vacuum FTIR spectrometer.The advantage of this technology has the following three points:firstly,RH controlling system can provide the change of relative humidity at different rates,the fastest can achieve 47%RH per second;secondly,vacuum technology can eliminate the effect of air and water vapor in the light path and we can get relative humidity values directly in the infrared spectrum to ensure the structure information of the sample and relative humidity are synchronous;thirdly,infrared scanning speed can be adjusted and the rapid scanning mode can realize a quick scan of the sample with microsecond time resolution to facilitate the study of the dynamic hygroscopic property of aerosols.The results are as follows:1.For the study of malonic aerosols,analysis of the features of FTIR absorbing bands found the evolution of hydrogen-bonding structures of malonic acid aerosols took place from（H₂O）_n-MA to MA-MA accompanying with phase transition in the dehumidifying process.In addition,the stepwise efflorescence of MA aerosols and nucleation rates at different RHs are first reported.Our observation has shown that the efflorescence of MA started at¹7%RH and the nucleation rates increased with decreasing RH.2.For the study of mixed NaNO₃/malonic aerosols with mole ratios 1:1,neither NaNO₃ nor malonic aerosols crystallize in the dehumidification process.Under fast RH changing rate,the mixed aerosols show obvious limiting water-transfer,which was caused by the viscous monosodium malonate produced by reaction between NaNO₃ and malonic.3.Three kinds of mixed aerosols MA/NaNO₃（1:1）,MA/Ca（NO₃）₂（1:1）and MA/Mg（NO₃）₂（1:1）have been investigated.We quantitatively estimated the absorbance value of COO^-、COOH and NO₃^-in the spectra of three kinds of mixed aerosols MA/NaNO₃（1:1）,MA/Ca（NO₃）₂（1:1）and MA/Mg（NO₃）₂（1:1）as a function of time at a certain RH and found NO₃^-loss is most for MA/Mg（NO₃）₂ aerosols.It showed that the reaaction degree of MA/Mg（NO₃）₂（1:1）is highest.