Investigating The Mechanism Of Atmospheric Multicomponent Nucleation Based On Flow Tube Experiment And Quantum Chemical Calculation

New Particle Formation(NPF)is a micro-scale evolution process from molecules to nanoparticles that affects air pollution,Earth's radiation balance,climate change,and human health at the regional and global scales.However,due to the diversity of the atmospheric environment and the limitations of current detection technologies,the mechanism leading to the formation of critical nucleus and subsequent growth is still unclear,especially the initial nucleation at the molecular level where critical nucleus are formed via phase transformation.Sulfuric acid is identified as one of the key nucleation precursors,but nucleation of H2SO4-H2O cannot explain atmospheric observations,and other species are needed.The components and mechanisms of organics involved in nucleation have been elusive.The nucleation rates simulated between theoretical calculations,laboratory simulations,and field observations are significantly different.An isolated method is no longer sufficient for microscopic nucleation studies.Therefore,it's significant under complex air pollution in China combining the flow tube experiment and theoretical calculations to study atmospheric organics-involved nucleation mechanism including the multi-component involved nucleation mechanism,i.e.,to identify the key nucleation precursors and to reveal the nucleation process.The main work and findings are as follows:1.A flow tube reaction system,equipped with advanced detection equipments and different home-made sampling devices,was designed and built.The robustness of the system was confirmed through sulfuric acid-water nucleation experiments.2.The effect of formaldehyde on sulfuric acid-water nucleation was studied by flow tube experiments and quantum chemistry.The experimental results reveal that the sulfuric acid-water homogeneous nucleation rate(J)at 297K is strongly dependent on[H2SO4]and humidity.J was slightly enhanced when adding CH2O of 0.31-2.40 ppb to stable H2SO4 and water system at 297K and variable humidity conditions.Cluster growth flux simulated from cluster dynamics model at experimental conditions indicates H2SO4-CH2O-based clusters are hard to grow.Therefore,the effect of CH2O on H2SO4-CH2O-H2O particle formation is weak and can be eliminated under atmospheric conditions.3.Structures,thermodynamics,hydration distribution,relative concentration of quaternary(NH3)(CH3NH2)(H2SO4)m(H2O)n(m=1-3,n=0-4)clusters involved multi-component nucleation were studied by quantum chemical calculations.We found that the proton transfers from H2SO4 molecule to CH3NH2 molecule is easier than to NH3 molecule forming ion pairs to stabilize and spontaneously form these clusters,thereby promoting nucleation.Synergistic effect of NH3 and amines might be important in forming the initial cluster with sulfuric acid and subsequently growth process.4.Structures,thermodynamics,kinetics,and atmospheric implications of quaternary(H2SO4)(TA)(B)(H2O)n(TA is tartaric acid,B is NH3 or dimethylamine,n=0-4)clusters involved dicarboxylic acid-based multi-component nucleation were studied by theoretical calculations.We found that the presence of TA triggers proton transfer from H2SO4 to the base molecule forming new covalent bonds or strengthens the preexisting covalent bonds to stabilize the cluster.Dipole-dipole interaction is not only positively related to clustering Gibbs energy change but also positively related to reaction rate constant.TA competes with H2SO4,NH3,CH3NH2 and dimethylamine to bond to H2SO4-based clusters under atmospherically relevant conditions.