Multicomponent Kinetic Model For Nucleation And Formation Mechanism Of PM_2.5 In Complex Air Pollution

Primary PM2 5(Particulate Matter with aerodynamic diameter smaller than 2.5?m)emissions from industry,agriculture and civilian are strictly controlled recently.The second PM2.5 and potential PM2.5 source have become the main bottleneck for haze pollution mitigation in China.The second PM2 5 constitutes the dominant responsibility for PM2.5 pollution,which is generated by precursors SO2,NOx,NH3 and VOCs(Volatile Organic Compound)through New Particle Formation(NPF).Nucleation is the fundamental step for NPF,but neither the H2SO4-H2O binary nor H2SO4-H2O-NH3 ternary nucleation model can describe the rapid NPF phenomenon in complex air with multiple and high-level pollutants.Therefore,based on the gas kinetic theory,a Multicomponent Kinetic Model(MKM)involving H2SO4,HNO3,NH3 and VOCs is established here to make up the gap.According to the MKM,the relation between PM2.5 and its precursors are revealed through identifying the role of NH3 and VOCs in NPF and finding the theoretical evidence for bacteria being involved in nucleation.Electric neutrality of PM2.5 is proposed based on the minimum energy principle.NH4+is found to be the key factor for charge balance in PM2.5,and the effect of ammonia on NPF enhancement is quantified.Micromorphology of single PM2.5 is reconstructed according to graph theory and Monte Carlo method.The organic compound is found to be the key factor for loose structure of PM2.5,and the bridging role of VOCs with different molecular structure in NPF is investigated.Based on the Density Function Theory(DFT),the hydrogen bond is found to be the driving force for aggregation of bacterium and PM2.5 precursors,and the potential ability of different bacteria to participate in NPF studied.Moreover,the incidental PM2.5 emissions from removing processes of NO,and SO2 are focused on.The PM2.5 formation mechanisms in Selective Catalytic Reduction(SCR)and Wet Flue Gas Desulfurization(WFGD)are revealed and the corresponding control strategies are proposed.To reduce PM2.5 pollution effectively,the NH3 and VOCs are suggested to be controlled to mitigate the secondary PM2.5,and reasonable operating parameters for SCR and WFGD are required to avoid unpredictable PM2.5 emission.