Simulation of particle size distribution with a global aerosol model: contribution of nucleation to aerosol and CCN number concentrations Atmospheric Sciences Research Center, State University of New York, 251 Fuller Road, Albany, New York 12203, USA
Received: 30 Mar 2009 – Published in Atmos. Chem. Phys. Discuss.: 30 Apr 2009Abstract. An advanced particle microphysics model with a number of
computationally efficient schemes has been incorporated into a global
chemistry transport model (GEOS-Chem) to simulate particle number size
distributions and cloud condensation nuclei (CCN) concentrations in the
atmosphere. Size-resolved microphysics for secondary particles (i.e., those
formed from gaseous species) and sea salt has been treated in the present
study. The growth of nucleated particles through the condensation of
sulfuric acid vapor and equilibrium uptake of nitrate, ammonium, and
secondary organic aerosol is explicitly simulated, along with the scavenging
of secondary particles by primary particles (dust, black carbon, organic
carbon, and sea salt). We calculate secondary particle formation rate based
on ion-mediated nucleation (IMN) mechanism and constrain the
parameterizations of primary particle emissions with various observations.
Our simulations indicate that secondary particles formed via IMN appear to
be able to account for the particle number concentrations observed in many
parts of the troposphere. A comparison of the simulated annual mean
concentrations of condensation nuclei larger than 10 nm (CN10) with those
measured values show very good agreement (within a factor of two) in near
all 22 sites around the globe that have at least one full year of CN10
measurements. Secondary particles appear to dominate the number abundance in
most parts of the troposphere. Calculated CCN concentration at
supersaturation of 0.4% (CCN0.4) and the fraction of CCN0.4 that is
secondary (fsecCCN) have large spatial variations. Over
the middle latitude in the Northern Hemisphere, zonally averaged CCN0.4
decreases from ~400–700 cm−3 in the boundary layer (BL) to below
100 cm−3 above altitude of ~4 km, the corresponding
fsecCCN values change from 50–60% to above ~70%.
In the Southern Hemisphere, the zonally averaged CCN0.4 is below
200 cm−3 and fsecCCN is generally above 60% except
in the BL over the Southern Ocean.
Revised: 18 Sep 2009 – Accepted: 28 Sep 2009 – Published: 16 Oct 2009
Citation: Yu, F. and Luo, G.: Simulation of particle size distribution with a global aerosol model: contribution of nucleation to aerosol and CCN number concentrations, Atmos. Chem. Phys., 9, 7691-7710, doi:10.5194/acp-9-7691-2009, 2009.