Improving new particle formation simulation by coupling a volatility-basis set (VBS) organic aerosol module in NAQPMS+APM

We developed a new modeling framework to simulate aerosol microphysics by incorporating a volatility basis-set (VBS) organic aerosol (OA) module into a three-dimensional (3-D) atmospheric transport model, namely, Nested Air Quality Prediction Modeling System with an Advanced Particle Microphysics (NAQPMS + APM). The new model calculates not only the condensation of sulfuric acid, nitrate, and ammonium and the coagulation of five types of particles (namely secondary, sea salt, dust, black carbon and organic carbon particles) but also the condensation of low-volatility organic vapors and the equilibrium partitioning of semi-volatile organic compounds. The new model was applied to simulate new particle formation (NPF) in summer in Beijing. The new model could noticeably improve the NPF simulation. On comparing the simulation with observation, the ion-mediated nucleation scheme was found to underestimate nucleation rates in summer in Beijing. By incorporating a nucleation formula involving the participation of organic compounds, NPF events could be reproduced satisfactorily. Reasonably calculating nucleation rates is essential for successfully simulating NPF. Accounting for the condensation of anthropogenic low-volatility organic vapors and the volatility of primary OA (POA) can improve the temporal variation of the number concentrations of particles in Aitken and accumulation modes. On a regional scale, anthropogenic low-volatility secondary organic gases (LV-SOGs) and the volatility of POA have large impacts on the aerosol number concentration and cloud condensation nuclei (CCN) concentration. Both anthropogenic LV-SOGs and volatility of POA must be considered to quantify the contribution of NPF to the aerosol number concentration and CCN concentration.