A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties

[摘要] A GLObal Model of Aerosol Processes (GLOMAP) has been developed as anextension to the TOMCAT 3-D Eulerian off-line chemical transportmodel. GLOMAP simulates the evolution of the global aerosol sizedistribution using a sectional two-moment scheme and includes theprocesses of aerosol nucleation, condensation, growth, coagulation,wet and dry deposition and cloud processing. We describe the resultsof a global simulation of sulfuric acid and sea spray aerosol. Themodel captures features of the aerosol size distribution that are wellestablished from observations in the marine boundary layer and freetroposphere. Modelled condensation nuclei (CN>3nm) vary betweenabout 250–500 cm^-3 in remote marine boundary layer regionsand are generally in good agreement with observations. Modelledcontinental CN concentrations are lower than observed, which may bedue to lack of some primary aerosol sources or the neglect ofnucleation mechanisms other than binary homogeneous nucleation ofsulfuric acid-water particles. Remote marine CN concentrationsincrease to around 2000–10 000 cm (at standardtemperature and pressure) in the upper troposphere, which agrees withtypical observed vertical profiles. Cloud condensation nuclei (CCN) at0.2% supersaturation vary between about 1000 cm^-3 in pollutedregions and between 10 and 500 cm^-3 in the remote marineboundary layer. New particle formation through sulfuric acid-waterbinary nucleation occurs predominantly in the upper troposphere, butthe model results show that these particles contribute greatly toaerosol concentrations in the marine boundary layer. For thissulfur-sea salt system it is estimated that sea spray emissionsaccount for only ~10% of CCN in the tropical marine boundarylayer, but between 20 and 75% in the mid-latitude Southern Ocean.In a run with only natural sulfate and sea salt emissions the globalmean surface CN concentration is more than 60% of that from a runwith 1985 anthropogenic sulfur emissions, although the naturalemissions comprise only 27% of total sulfur emissions. Southernhemisphere marine boundary layer CN are more than 90% natural inorigin, while polluted continental CN are more than 90% anthropogenicin origin, although these numbers will change when other anthropogenicCN sources are included in the model.

[学科分类] 大气科学