Comprehensive simulations of new particle formation events in Beijing with a cluster dynamics-multicomponent sectional model

New particle formation (NPF) and growth are a major source of atmosphericfine particles. In polluted urban environments, NPF events are frequentlyobserved with characteristics distinct from those in clean environments.Here we simulate NPF events in urban Beijing with a discrete-sectional model that couples cluster dynamics and multicomponent particle growth. In the model, new particles are formed by sulfuric acid-dimethylamine nucleation, while particle growth is driven by particle coagulation and the condensationof sulfuric acid, its clusters, and oxygenated organic molecules (OOMs). Avariable simulation domain in the particle size space is applied to isolatenewly formed particles from preexisting ones, which allows us to focus onnew particle formation and growth rather than the evolution of particles ofnon-NPF origin. The simulation yields a rich set of information includingthe time-dependent NPF rates, the cluster concentrations, the particle sizedistributions, and the time- and size-specific particle chemicalcompositions. These can be compared with the field observations tocomprehensively assess the simulation-observation agreement. Sensitivityanalysis with the model further quantifies how metrics of NPF events (e.g.,particle survival probability) respond to model input variations and servesas a diagnostic tool to pinpoint the key parameter that leads tosimulation-observation discrepancies. Seven typical NPF events in urbanBeijing were analyzed. We found that with the observed gaseous precursorconcentrations and coagulation sink as model inputs, the simulations roughly captured the evolution of the observed particle size distributions; however,the simulated particle growth rate was insufficient to yield the observedparticle number concentrations, survival probability, and mode diameter.With the aid of sensitivity analysis, we identified under-detected OOMs as alikely cause for the discrepancy, and the agreement between the simulationand the observation was improved after we modulated particle growth rates in the simulation by adjusting the abundance of OOMs.