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Simulating aerosol microphysics with the ECHAM4/MADE GCM – Part II: Results from a first multiannual simulation of the submicrometer aerosol

by A. Lauer, J. Hendricks
Atmospheric Chemistry and Physics ()

Abstract

First results of a multiannual integration with the new global aerosol\nmodel system ECHAM4/MADE are presented. This model system enables\nsimulations of the particle number concentration and size-distribution,\nwhich is a fundamental innovation compared to previous global model\nstudies considering aerosol mass cycles only. The data calculated\nby the model provide detailed insights into the properties of the\nglobal submicrometer aerosol regarding global burden, chemical composition,\natmospheric residence time, particle number concentration and size-distribution.\nThe aerosol components considered by the model are sulfate (SO4),\nnitrate (NO3), ammonium (NH4), black carbon (BC), organic matter\n(OM), mineral dust, sea salt and aerosol water. The simulated climatological\nannual mean global atmospheric burdens (residence times) of the dominant\nsubmicrometer aerosol components are 2.25 Tg (4.5 d) for SO4, 0.46\nTg (4.5 d) for NH4, 0.26 Tg (6.6 d) for BC, and 1.77 Tg (6.5 d) for\nOM. The contributions of individual processes such as emission, nucleation,\ncondensation or dry and wet deposition to the global sources and\nsinks of specific aerosol components and particle number concentration\nare quantified. Based on this analysis, the significance of aerosol\nmicrophysical processes (nucleation, condensation, coagulation) is\nevaluated by comparison to the importance of other processes relevant\nfor the submicrometer aerosol on the global scale. The results reveal\nthat aerosol microphysics are essential for the simulation of the\nparticle number concentration and important but not vital for the\nsimulation of particle mass concentration. Hence aerosol microphysics\nshould be taken into account in simulations of atmospheric processes\nshowing a significant dependence on aerosol particle number concentration.\nThe analysis of the vertical variation of the microphysical net production\nand net depletion rates performed for particle number concentration,\nsulfate mass and black carbon mass concentration unveils the dominant\nsource and sink regions. Prominent features can be attributed to\ndominant microphysical processes such as nucleation in the upper\ntroposphere or wet deposition in the lower troposphere. Regions of\nefficient coagulation can be identified.

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