Global–regional nested simulation of particle number concentration by combing microphysical processes with an evolving organic aerosol module

Abstract

Abstract. Aerosol microphysical processes are essential for the next generation of\nglobal and regional climate and air quality models to determine particle\nsize distribution. The contribution of organic aerosols (OAs) to particle\nformation, mass, and number concentration is one of the major uncertainties\nin current models. A new global–regional nested aerosol model was developed\nto simulate detailed microphysical processes. The model combines an advanced\nparticle microphysics (APM) module and a volatility basis set (VBS) OA\nmodule to calculate the kinetic condensation of low-volatility organic\ncompounds and equilibrium partitioning of semi-volatile organic compounds in\na 3-D framework using global–regional nested domain. In\naddition to the condensation of sulfuric acid, the equilibrium partitioning\nof nitrate and ammonium, and the coagulation process of particles, the\nmicrophysical processes of the OAs are realistically represented in our new\nmodel. The model uses high-resolution size bins to calculate the size\ndistribution of new particles formed through nucleation and subsequent\ngrowth. The multi-scale nesting enables the model to perform high-resolution\nsimulations of the particle formation processes in the urban atmosphere in\nthe background of regional and global environments. By using the nested\ndomains, the model reasonably reproduced the OA components obtained from the\nanalysis of aerosol mass spectrometry measurements through positive matrix\nfactorization and the particle number size distribution in the megacity of\nBeijing during a period of approximately a month. Anthropogenic organic\nspecies accounted for 67\u2009% of the OAs of secondary particles formed by\nnucleation and subsequent growth, which is considerably larger than that of\nbiogenic OAs. On the global scale, the model well predicted the particle\nnumber concentration in various environments. The microphysical module\ncombined with the VBS simulated the universal distribution of organic\ncomponents among the different aerosol populations. The model results\nstrongly suggest the importance of anthropogenic organic species in aerosol\nparticle formation and growth at polluted urban sites and over the whole\nglobe.\n