Theoretical Study Of Aerosol Nucleation Involving Organic Acids And Development Of The Photoelectron Spectroscopy Instrument

Atmospheric aerosols are particulate matter suspended in the air that has profound effects on visibility,human health and global climate.New particle formation(NPF)is an important source of atmospheric aerosols,including two stages of nucleation and growth.Although NPF events are frequently studied,there are still many uncertainties,especially in the nucleation stage of the formation of critical nuclei from gas phase precursors.Organic acids are expected to be involved in NPF,and two common organic acids(oxalic acid and methanesulfonic acid)were selected for discussion in this paper.Oxalic acid,one of the most common organic acids in the Earth's atmosphere,is believed to enhance the nucleation and growth of nanoparticles by binding sulfuric acid and water.However,there is a lack of detailed studies on oxalic acid-sulfuric acid hydrates currently,and the understanding of large-size clusters containing more water molecules is particularly insufficient.We studied the structural characteristics and thermodynamics of the clusters using density functional theory at the PW91PW91/6?311++G(3df,3pd)level.The results show that:(1)At the temperature of 298.15 K,the favorable free energy of formation and significant concentration for the oxalic acid-sulfuric acid-water clusters indicate that oxalic acid can promote the nucleation process of aerosols by combining sulfuric acid and 0-6 waters.(2)Lower temperature and higher relative humidity promote the formation of hydrates.(3)In addition,we systematically studied the Rayleigh scattering properties of oxalic acid-sulfuric acid-water clusters for the first time to further discuss their atmospheric implication.Additionally,methanesulfonate,ammonia/amine and water were selected to investigate the role of ternary nucleation and ion-induced nucleation in aerosol formation.Through the research of this system,we discover that:(1)Methanesulfonate forms aerosol clusters by binding ammonia or amine with 1 to 3 water molecules.(2)Although amines are more easily associated with methanesulfonate than ammonia,there are more methanesulfonate-ammonia clusters in the atmosphere.(3)Based on the analysis of evaporation rate,ammonia or amines could be evaporated more easily than methanesulfonate and water molecules,and the presence of water significantly affects the evaporation rate of methanesulfonate,ammonia or amine.The structure of molecular clusters can be obtained by quantum chemistry theoretical calculations,in order to further determine the structure information of these clusters in the experiment,the corresponding measuring instruments are needed.However,for aerosol,the common observation equipment is mainly used to detect the concentration of aerosol above 3 nm,but for the nucleation stage below 3 nm,there is no corresponding measurement equipment.Recently,there have been several mass spectrometers available for nucleation studies.These instruments may be able to observe the nucleation clusters,but it is difficult to determine the exact composition of these clusters.Therefore,we combined the mass spectrometer and the photoelectron spectroscopy to develop a mass spectrometry-photoelectron spectroscopy apparatus that can effectively expand the research field of mass spectrometers.Through the mass spectrometry-photoelectron spectroscopy apparatus,both mass spectrometry and photoelectron spectroscopy information can be obtained to get the structure and composition information of the substance.In the apparatus,the mass spectrometer is based on ion trap mass analyzers and electrospray ionization sources.The mass spectrometer can perform positive and negative ion mass analysis,mass isolation,and collision-induced dissociation.Its detection range of mass is greater than 2,000 Th.The photoelectron spectrometer is mainly composed of a vacuum chamber,an ion focusing deflection device,a set of velocity-map imaging lens and a laser system,and its energy resolution is about 6%.The mass spectrometer-photoelectron spectrometer apparatus is small in size and can be used in the field research of atmospheric aerosol nucleation.