Study On The Hygroscopicity And Volatility Of Mixed Organic/Inorganic Aerosol By Infrared Spectroscopy

With the rapid expansion and urbanization in our country,aerosol pollution in the atmosphere has become a critical environmental problem.Gas-particle equilibrium and partition are important physical and chemical courses on the formation and evolution of atmospheric particulates,which involves hygroscopicity and volatility of atmospheric aerosol.Hygroscopicity and volatility are the important properties of atmospheric aerosols which depend on the chemical components,relatively humidity and gas phase compositon,have attracted intense scientific interest.In this thesis,FTIR is used to investigate the hygroscopicity and volatility of several organic and mixed organic/inorganic aerosol particles and the following is the main conclusion.(1)Hygroscopicity of Magnesium Acetate Aerosols-Cooperation Between CH₃COOH Volatilization and Mg²⁺HydrolysisA combination of a vacuum FTIR spectrometer and a home-made relative humidity(RH)controlling system to was used to investigate the hygroscopic property of magnesium acetate(Mg(Ac)₂)aerosol when the relative humidity(RH)was changed with stepwise mode and pulsed mode at elevated RH.At constant 90%RH and 80%RH for 3000 seconds,the water content within Mg(Ac)₂ aerosols decreased about 19.0%and 9.4%while the peak area of acetate ions(Ac^-)reduced about 13.4%and 6.0%.Mg²⁺hydrolysis at elevated RH was driven by evaporation of HAc,which resulted in the formation of low solubility magnesium hydroxide(Mg(OH)₂).The evaporation of HAc was further promoted by the hydrolysis reaction in turn.And then,the cooperation between volatile of acetic acid and Mg²⁺hydrolysis in Mg(Ac)₂ aerosols greatly suppressed the hygroscopicity of Mg(Ac)₂ aerosols.In addition,When the RH was changed with pulsed mode between 70%and 90%,hygroscopicity relaxation was observed for Mg(Ac)₂ aerosols.Diffuse coefficient of water was estimated to be 5×10^-12 m²×s^-1in the relaxation process in the aerosols.Decrease in the diffuse coefficient of water was due to the formation of magnesium hydroxide accompanying acetic acid evaporation in the aerosols.The results showed that he release of HAc at high RH may have significant effects on acetate-acetic acid partition and its atmospheric budget.(2)The hygroscopicity studies of the internally mixed water-soluble carboxylic salts-(NH₄)₂SO₄ aqueous droplets:volatile of NH₃ and formation of dicarboxylic acidThe hygroscopic behaviors of atmospherically relevant water-soluble carboxylic salts and their mixtures with(NH₄)₂SO₄ were investigated using attenuated total reflection Fourier transform infrared spectroscopy(FTIR-ATR).The mixed disodium succinate/(NH₄)₂SO₄aerosol particle was used as a sample in order to reveal the relationship between hygrosocopicity and different OIRs.The results showed that disodium succinate and disodium malonate can react with(NH₄)₂SO₄,respectively,resulting in the release of gaseous NH₃ and formation of succinic acid and malonic acid during the hydration process.Among the investigated carboxylic salts species,disodium oxalate can not react with(NH₄)₂SO₄.By comparing the hygroscopicity of relevant reactants and products,it found that these reactions were attributed to the formation of low hygroscopicity organic acid and the evaporation of NH₃ into gas phase.In addition,our results also suggested that the chemical reaction between disodium succinate and(NH₄)₂SO₄ with different OIRs could result in the formation of less hygroscopic succinic acid(OIR=1:3 and 1:1)or monosodium succinate(OIR=3:1)and volatility of NH₃,which decreases the hygroscopicity of particles.These results could contribute to understanding of mutual transformation process between dicarboxylic acids and carboxylate salts as well as reveal a potential mechanism of NH₃ recycling in the atmosphere.(3)Hygroscopicity of internally mixed aerosol particles containing NaCl and glycineThe hygroscopicity of glycine and its mixture with NaCl at different OIRs was studied by the FTIR-ATR.The glycine started absorb a small amount of water at low RH but exhibited a non-deliquescent behavior even at higher RH.This might be due to the capillary effects of the small cracks on the solid particle surface.The polymorphism of glycine was changed due to the salting-in effect induced by the added NaCl.In addition,with the increasing of RH,the deliquescence relative humidity(DRH)of glycine were observed at79.7%RH and 79%RH for OIRs were 1:3 and 1:1,respectively.Interesting,the glycine exhibits a non?deliquescent behavior at the OIR is 3:1 whereas the DRH of NaCl was decreased from 80.8%to72.9%.These results indicated that the presence of NaCl lowered the DRH of glycine and altered its deliquescence process and vice versa.The decline of DRH was proposed to arise from the ion-molecule interactions between the inorganic and organic components.The results implied that the effect between inorganic and organic components was mutual.