Contribution of primary carbonaceous aerosol to cloud condensation nuclei: processes and uncertainties evaluated with a global aerosol microphysics model

[摘要] This paper explores the impacts of primary carbonaceous aerosol on cloudcondensation nuclei (CCN) concentrations in a global climate model withsize-resolved aerosol microphysics. Organic matter (OM) and elemental carbon(EC) from two emissions inventories were incorporated into a preexistingmodel with sulfate and sea-salt aerosol. The addition of primary carbonaceousaerosol increased CCN(0.2%) concentrations by 65–90% in the globallyaveraged surface layer depending on the carbonaceous emissions inventoryused. Sensitivity studies were performed to determine the relativeimportance of organic solubility/hygroscopicity in predicting CCN.In a sensitivity study where carbonaceous aerosol was assumed to be completely insoluble, concentrationsof CCN(0.2%) still increased by 40–50% globally over the nocarbonaceous simulation because primary carbonaceous emissions were able tobecome CCN via condensation of sulfuric acid. This shows that approximatelyhalf of the contribution of primary carbonaceous particles to CCN in our modelcomes from the addition of new particles (seeding effect) and half from the contribution oforganic solute (solute effect). The solute effecttends to dominate more in areas where there is less inorganic aerosol thanorganic aerosol and the seeding effect tends to dominate in areas where there ismore inorganic aerosol than organic aerosol. It was found that an accuratesimulation of the number size distribution is necessary to predict the CCNconcentration but assuming an average chemical composition will generallygive a CCN concentration within a factor of 2. If a "typical" sizedistribution is assumed for each species when calculating CCN, such as isdone in bulk aerosol models, the mean error relative to a simulation withsize resolved microphysics is on the order of 35%. Predicted values ofcarbonaceous aerosol mass and aerosol number were compared to observationsand the model showed average errors of a factor of 3 for carbonaceous massand a factor of 4 for total aerosol number; however, errors in the accumulationmode concentrations were found to be lower in comparisons with European andmarine observations.. The errors in CN and carbonaceous mass may be reduced byimproving the emission size distributions of both primary sulfate andprimary carbonaceous aerosol.

[学科分类] 大气科学