Abstract. The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.

Abstract. The aerosol-climate modelling system ECHAM5-HAM is introduced. It is based on a flexible microphysical approach and, as the number of externally imposed parameters is minimised, allows the application in a wide range of climate regimes.

Abstract. Inventories for global aerosol and aerosol precursor emissions have been collected (based on published inventories and published simulations), assessed and prepared for the year 2000 (present-day conditions) and for the year 1750 (pre-industrial conditions). These global datasets establish a comprehensive source for emission input to global modeling, when simulating the aerosol impact on climate with state-of-the-art aerosol component modules. As these modules stratify aerosol into dust, sea-salt, sulfate, organic matter and soot, for all these aerosol types global fields on emission strength and recommendations for injection altitude and particulate size are provided. Temporal resolution varies between daily (dust and sea-salt), monthly (wild-land fires) and annual (all other emissions). These datasets benchmark aerosol emissions according to the knowledge in the year 2004. They are intended to serve as systematic constraints in sensitivity studies of the AeroCom initiative, which seeks to quantify (actual) uncertainties in aerosol global modeling.

[1] An aerosol model (M7) designed to be coupled to general circulation models (GCM) and chemistry transport models (CTM) is described. In M7 the aerosol population is divided into two types of particles: mixed, or water-soluble particles, and insoluble particles. The particles are represented by seven classes, using a ''pseudomodal'' approach. Four classes are for the mixed particles representing nucleation, Aitken, accumulation, and coarse mode, and three are for the insoluble (Aitken, accumulation, and coarse mode). The components considered are mineral dust, black carbon (BC) and primary organic carbon (OC), sulfate, and sea salt. The aerosol dynamic processes in M7 include nucleation, coagulation, and condensation of sulfuric acid. Mixed particles are formed from insoluble particles by coagulation and condensation. The integration scheme is computationally very efficient. The model has been tested against the analytical solution and a sectional model for the formation of SO 4 /BC mixed particles, evaluating the mixing by condensation and coagulation. Furthermore, M7 has been run in free tropospheric conditions and compared to aircraft observations. M7 has proven to be accurate and fast enough to be included in a GCM or CTM.

A global inventory has been constructed for emissions of black carbon from fossil fuel combustion and biomass burning. This inventory has been implemented in a three‐dimensional global transport model and run for 31 model months. Results for January and July have been compared with measurements taken from the literature. The modeled values of black carbon mass concentration compare within a factor of 2 in continental regions and some remote regions but are higher than measured values in other remote marine regions and in the upper troposphere. The disagreement in remote regions can be explained by the coarse grid scale of the model (10° × 10°), the simplicity of the current deposition scheme, and possibly too much black carbon being available for transport, which would also account for the disagreement in the upper troposphere. The disagreement may also be due to problems associated with the measurement of black carbon. Emissions from this database appear to provide a reasonable estimate of the annual emissions of black carbon to the atmosphere. Biomass burning emissions amount to 5.98 Tg and that from fossil fuel amounts to 7.96 Tg. A local sensitivity analysis has been carried out and shows that black carbon has a lifetime between 6 and 10 days, depending on the transformation rate between hydrophobic and hydrophilic black carbon.

Abstract. Inventories for global aerosol and aerosol precursor emissions, and auxiliary information, have been collected, assessed and prepared for the year 2000 (present-day conditions) and for the year 1750 (pre-industrial conditions). These global datasets establish a reference for input in global modeling, when simulating the aerosol impact on climate with state-of-the-art aerosol component modules. These modules stratify aerosol by type, distinguishing among dust, seasalt, sulfate, organic matter and soot. The datasets are also intented to serve as systematic constraints in sensitivity studies of the AeroCom initiative, which aims to evaluate uncertainties in aerosol global modeling. The datasets comprise daily size-resolved emissions of sea-salt and dust and monthly-to-yearly emissions for all other currently known emissions of natural and anthropogenic aerosol (precursors). The emissions are a reference dataset for aerosol modeling in the coming years and benchmark the emissions according to our knowledge in the year 2004.

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Abstract. Our understanding of the global black carbon (BC) cycle is essentially qualitative due to uncertainties in our knowledge of its properties. This work investigates two source of uncertainties in modelling black carbon: those due to the use of different schemes for BC ageing and its removal rate in the global Transport-Chemistry model TM5 and those due to the uncertainties in the definition and quantification of the observations, which propagate through to both the emission inventories, and the measurements used for the model evaluation.The schemes for the atmospheric processing of black carbon that have been tested with the model are (i) a simple approach considering BC as bulk aerosol and a simple treatment of the removal with fixed 70% of in-cloud black carbon concentrations scavenged by clouds and removed when rain is present and (ii) a more complete description of microphysical ageing within an aerosol dynamics model, where removal is coupled to the microphysical properties of the aerosol, which results in a global average of 40% in-cloud black carbon that is scavenged in clouds and subsequently removed by rain, thus resulting in a longer atmospheric lifetime. This difference is reflected in comparisons between both sets of modelled results and the measurements. Close to the sources, both anthropogenic and vegetation fire source regions, the model results do not differ significantly, indicating that the emissions are the prevailing mechanism determining the concentrations and the choice of the aerosol scheme does not influence the levels. In more remote areas such as Correspondence to: E. Vignati (elisabetta.vignati@jrc.ec.europa.eu) oceanic and polar regions the differences can be orders of magnitude, due to the differences between the two schemes. The more complete description reproduces the seasonal trend of the black carbon observations in those areas, although not always the magnitude of the signal, while the more simplified approach underestimates black carbon concentrations by orders of magnitude.The sensitivity to wet scavenging has been tested by varying in-cloud and below-cloud removal. BC lifetime increases by 10% when large scale and convective scale precipitation removal efficiency are reduced by 30%, while the variation is very small when below-cloud scavenging is zero.Since the emission inventories are representative of elemental carbon-like substance, the model output should be compared to elemental carbon measurements and if known, the ratio of black carbon to elemental carbon mass should be taken into account when the model is compared with black carbon observations.