Raman Spectroscopic Studies On The Hygroscopicity Of Mixed Organic/Inorganic Aerosol

The types and quantity of atmospheric aerosol particles are important factors leading to thehaze and atmospheric pollution. Organic aerosols typically constitute approximately10-70%of the total dry fine particle mass in the atmosphere. The study on hygroscopicity of mixedorganic/inorganic aerosol particles is significant to the understanding of the formationmechanism of haze. In this paper, we researched on the hygroscopicity of several importantmixed organic/inorganic aerosol particles by the using of confocal Raman spectroscopicmethod. The results are as follows:Firstly, We researched Raman spectra of mixed phthalic acid/(NH4)2SO4aerosoldroplets during the dehumidifying process. By comparing Raman spectra with high spatialresolution collacted from the mixed droplet, we know the phase separation of organic andinorganic phases. We propose that the salting-out effect may induce the diffusion oforganics from the center of the droplet to the surface and the formation of the organicsphase, thus lead to liquid-liquid phase separation (LLPS) in aerosol droplets. When themixed droplet is dropped on the hydrophilic substrate the organics is the inner phase andthe outer is (NH4)2SO4, which is different from the state of aerosol dropping on thehydrophobic substrate. We give a new point that the effect of substrates will influence thespatial distribution of organic/inorganic components in aerosols. Both the surface tensionand effect of substrates influence the physical state of mixed organic/inorganic aerosols.Secondly, we also studied the the efflorescence of NaNO3droplets and mixed ethyleneglycol/NaNO3droplets with different OIR on the hydrophobic substrate. The results showthat the addition of ethylene glycol inhibited the efflorescence of NaNO3droplets. In mixedethylene glyco/NaNO3droplets, there exist interactions between ethylene glycol and Na+and NO3-ions. Na+and NO3-can combine with ethylene glycol molecules into relativelystable complexs through electrostatic force and hydrogen bond interactions. With theincrease of ethylene glycol content in the mixed droplets, the number of Na+and NO3-combined with ethylene glycol molecules increases, resulting in the formation of morestable complexes, thereby inhibiting the efflorescence of NaNO3droplets. Finally, we also focus on the rules of the conformation of ethylene glycol molecularand hydrogen bonding during the process of temperature variation. The ethyleneglycol/water binary system simulates the composition of airport deicing agent, motorvehicle antifreeze and cryoprotectant. By the analysis of the spectral region of themolecular vibration (νC-O, νC-C) and hydroxyl vibration, we obtained the variation law ofethylene glycol molecular conformation and hydrogen bond (H-bond) during the process oftemperature variation. During the cooling process, ethylene glycol molecules conformationtransform from trans-to gauche-conformation and H-bonds transform from―longerH-bonds‖and―middle H-bonds‖to―shorter H-bonds‖. During the heating process, thetrend is exactly shown as the opposite. We summarize the principle of ethylene glycol asantifreeze. Between ethylene glycol and water molecules there exists a large number ofH-bonds, which destroys H-bonds between water molecules, and thus impedes thethree-dimensional network of hydrogen bonding structure of ice formed between watermolecules, reduces the water’s freezing point.