Enhancing particle number concentration modelling accuracy in China by incorporating various nucleation parameterization schemes into the CMAQ version 5.3.2 model

Abstract. Particle number concentration (PNC) is a key parameter for assessing particles’ effects on public health and climate. Although the Community Multiscale Air Quality (CMAQ) model has been widely used to investigate the particle mass concentrations in China, its capability of reproducing the PNC is unclear. After applying the default CMAQ model (version 5.3.2) in Beijing and Nanjing, the model underestimates PNC by 70 % to 80 % with the default Binary Homogeneous Nucleation (BHN) parameterization scheme. We then implement Ternary Homogeneous Nucleation (THN), Ion Mediated Nucleation (IMN), and H₂SO₄-dimethylamine (DMA) nucleation parameterization schemes into the CMAQ model. Seven modelling scenarios are conducted to explore the model's performance on PNC. The results indicate that the scenario with combined IMN and DMA scheme (SumID scheme) yields the best agreement with the observations, enhancing PNC during new particle formation (NPF) events by 84 % in Beijing and 36 % in Nanjing. In SumID scheme, IMN contributes to 56.30 % of the number concentrations in Beijing and 27.86 % in Nanjing, while DMA accounts for 28.15 % in Beijing and 29.27 % in Nanjing, respectively. IMN nucleation contributed PNC exhibits a pronounced diurnal variation with higher concentrations during the day and lower levels at night. DMA pathway predominantly influences NPF events during the morning and evening peak. This study enhances the model's capability to accurately simulate NPF events and underscores the significant influence of IMN and DMA nucleation on PNC in China.