Study The Hygroscopicity,nucleation And Mass Transfer Of Aerosols Composed Of Organic Compounds And Inorganic Salts

The study of hygroscopicity,nucleation and mass transfer of atmospheric aerosol is very important for people to understand the climate change,atmospheric pollution and human health.In this study,a pulsed relative humidity controlling system and a rapid scan vacuum FTIR spectrometer?PRHCS-RSVFTIR?and hygroscopicity tandem differential mobility analyzer?HTDMA?are used to measure the thermodynamic?hygroscopicity?and dynamic process?nucleation,mass transfer?of various organic and inorganic.The following are the main conclusions.?1?The hygroscopicity and nucleation kinetics of mixed aerosol composed of ammonium sulfate?AS?/citric acid?CA?is studied by using PRHCS-RSVFTIR technique.We observed the FTIR spectra changes of AS/CA mixed aerosol droplets in the equilibrium and relative humidity pulsed processes by changing the relative humidity?RH?rates.Under downward RH pulsed process,AS particles present stepwise efflorescence,and the result of the RH pulsed process is generally in agreement with the equilibrium process?0.1RH/s?.For the molar ratio of AS:CA=1:1,1:3,the addition of citric acid changes the hygroscopicity of AS completely,and no efflorescence occurrence is detected.For the molar ratio of AS:CA=3:1,the addition of citric acid inhibits the efflorescent process of AS.The ERH range of mixed AS/CA?3:1?droplets is enlarged compared to pure AS droplets.For the first time,heterogeneous nucleation rates of?NH₄?₂SO₄ are obtained for the internally mixed particles and the value is decreased almost three orders of magnitude when citric acid exists at a certain RH.?2?The water transfer limitation of mixed aerosol composed of AS/CA is studied by using PRHCS-RSVFTIR technique.Citric acid particles show neither crystallization nor deliquescence in equilibrium process?hydration and dehydration?,and take up or release water reversibly.While in the RH pulsed processes,both rapid humidification and dehumidification curves are not merged below 40%RH and there exists delay in water uptake.We quantitatively analyzed the ratio of half-time of liquid water content to half-time of RH changes,and the result shows that water transfer limitaton is more obvious below 20%RH.Two possible different mechanism is speculated at RH<20%and 20%<RH<40%.The water diffusion constants below 40%RH are obtained by applying the pulsed RH change method.For the first time,water diffusion constants between 10^-12 m² s^-1 and 10^-13m² s^-1in citric acid aerosols are obtained.Besides,water diffusion constants of AS/CA mixtures with molar ratios AS:CA=1:3 are also researched.The study indicates that the presence of AS enhances the water transfer limitation in CA aerosol.?3?The hygroscopic growth of ammonium nitrate/oxalic acid,ammonium nitrate/succinic acid and ammonium nitrate/phthalic acid is measured by using the H-TDMA system.ZSR method is used to predict the hygroscopic growth of the mixed particles at different RH.The results show that the hygroscopicity of internally mixed aerosols can be affected by the different state and composition.The water uptake behavior of ammonium nitrate can be affected due to the exist of oxalic acid,succinic acid and phthalic acid,which in turn influence the activity of cloud condensation nuclei,optical properties and chemical reactivity.