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An advanced particle microphysics model with a number ofcomputationally efficient schemes has been incorporated into a globalchemistry transport model (GEOS-Chem) to simulate particle number sizedistributions and cloud condensation nuclei (CCN) concentrations in theatmosphere. Size-resolved microphysics for secondary particles (i.e., thoseformed from gaseous species) and sea salt has been treated in the presentstudy. The growth of nucleated particles through the condensation ofsulfuric acid vapor and equilibrium uptake of nitrate, ammonium, andsecondary organic aerosol is explicitly simulated, along with the scavengingof secondary particles by primary particles (dust, black carbon, organiccarbon, and sea salt). We calculate secondary particle formation rate basedon ion-mediated nucleation (IMN) mechanism and constrain theparameterizations of primary particle emissions with various observations.Our simulations indicate that secondary particles formed via IMN appear tobe able to account for the particle number concentrations observed in manyparts of the troposphere. A comparison of the simulated annual meanconcentrations of condensation nuclei larger than 10 nm (CN10) with thosemeasured values show very good agreement (within a factor of two) in nearall 22 sites around the globe that have at least one full year of CN10measurements. Secondary particles appear to dominate the number abundance inmost parts of the troposphere. Calculated CCN concentration atsupersaturation of 0.4% (CCN0.4) and the fraction of CCN0.4 that issecondary (fsecCCN) have large spatial variations. Overthe middle latitude in the Northern Hemisphere, zonally averaged CCN0.4decreases from ~400–700 cm−3 in the boundary layer (BL) to below100 cm−3 above altitude of ~4 km, the correspondingfsecCCN values change from 50–60% to above ~70%.In the Southern Hemisphere, the zonally averaged CCN0.4 is below200 cm−3 and fsecCCN is generally above 60% exceptin the BL over the Southern Ocean

Simulation of particle size distribution with a global aerosol model: contribution of nucleation to aerosol and CCN number concentrations