New Particle Formation And Long-term Trend Modeling Number Concentration In Chinese Typical Cities

New Particle Formation（NPF）refers to a process in which condensable gas in the atmosphere forms critical molecular clusters and grows to form ultrafine-fine particles.In order to evaluate the impact of NPF,Community Multiscale Air Quality model（CMAQ）has been used to simulate regional NPF events in this study.In the model,the number concentration is underpredicted,which means Binary Homogeneous Nucleation（BHN）can’t reproduce NPF.Ternary Homogeneous Nucleation（THN）,Ion-Mediated Nucleation（IMN）,and sulfuric acid-Dim Methyl Amine nucleation（DMA）nucleation are implemented into model.Six nucleation scenarios are established to simulate two NPF events in Beijing and Nanjing with evaluation for selecting the best scenario.Based on the updated model,long-term trend modeling number concentration from 2013 to 2019 is simulated in Beijing with evaluation and trend analysis.The NPF days and non-NPF days are analyzed with observation and simulation.The study shows that BHN underpredicts number concentration obviously;DMA simulates well at night;THN and IMN show similarly.IMN and DMA considered together is the best scheme under comparation.In this scheme,IMN dominates daytime NPF and DMA is the night.The updated model can reproduce number concentration and trends in Beijing from2013 to 2019.The observed trend of number concentration increased during 2013-2014 and decreased during 2015-2019,and the model reproduced the trends during 2014-2018.In seasonal,R in summer is under 0.3 and NMB in winter is under 0.5.In NPF days,the frequency of NPF occurrence is 38%in 2014,with 10 cm^-3 s^-1 median nucleation rate;although the frequency occurrence is 17.5%in 2018,its highly nucleation rate is near 100 cm^-3 s^-1.Summer has 23.6%frequency in NPF days with over 50 cm^-3 s^-1 average nucleation rate;winter has36.67%frequency,while its median nucleation rate is only 10 cm^-3 s^-1.In nucleation pathway,DMA dominates 95%in summer and IMN dominates over 98%in winter.This study validates the ability of the updated model in simulating NPF events and finds that IMN and DMA nucleation contribute number concentration importantly in Chinese cities.This study can provide theoretical basis and results for evaluating the relationship between NPF events,haze formation and atmospheric oxidation capability in the future.At the same time,the model can be used as a tool to simulate the relative contributions of different nucleation mechanisms in NPF.