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[1] The impact of the heterogeneous hydrolysis of N 2 O 5 on tropospheric gas phase and particle phase chemistry was investigated by performing model simulations with two comprehensive model systems and taking into account recent findings on the heterogeneous reaction probability of N 2 O 5 . Hereby, we focused on photosmog conditions in the lower troposphere. Chemistry box model runs were carried out neglecting transport and deposition processes. The heterogeneous hydrolysis of N 2 O 5 leads to a decrease of ozone under low-NO x conditions and to a strong increase of ozone under high-NO x conditions. One-dimensional simulations were performed to take into account vertical mixing processes, deposition, and temporal changes of the emissions. The rate constant for the heterogeneous hydrolysis was determined depending on the simulated aerosol surface area density. A large impact of the heterogeneous hydrolysis on the nocturnal concentrations of N 2 O 5 , NO 3 , HNO 3 , and the surface area density and nitrate content of the aerosol is found. However, the effect of the hydrolysis of N 2 O 5 on ozone decreases considerably compared to the box model simulations. Three-dimensional simulations for a typical summer smog situation for the southwestern part of Germany and on the European scale, which cover a variety of atmospheric and emission conditions, confirm these findings. The impact of heterogeneous hydrolysis on ozone is small, but it causes remarkable changes in the nocturnal concentrations of nitrogen-containing species and on aerosol properties such as surface area density and nitrate content.

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Abstract. The aerosol dynamics module MADE has been coupled to the general circulation model ECHAM4 to simulate the chemical composition, number concentration, and size distribution of the global submicrometer aerosol. The present publication describes the new model system ECHAM4/MADE and presents model results in comparison with observations. The new model is able to simulate the full life cycle of particulate matter and various gaseous particle precursors including emissions of primary particles and trace gases, advection, convection, diffusion, coagulation, condensation, nucleation of sulfuric acid vapor, aerosol chemistry, cloud processing, and size-dependent dry and wet deposition. Aerosol components considered are sulfate (SO 4 ), ammonium (NH 4 ), nitrate (NO 3 ), black carbon (BC), particulate organic matter (POM), sea salt, mineral dust, and aerosol liquid water. The model is numerically efficient enough to allow long term simulations, which is an essential requirement for application in general circulation models. Since the current study is focusing on the submicrometer aerosol, a coarse mode is not being simulated. The model is run in a passive mode, i.e. no feedbacks between the MADE aerosols and clouds or radiation are considered yet. This allows the investigation of the effect of aerosol dynamics, not interfered by feedbacks of the altered aerosols on clouds, radiation, and on the model dynamics.In order to evaluate the results obtained with this new model system, calculated mass concentrations, particle number concentrations, and size distributions are compared to observations. The intercomparison shows, that ECHAM4/MADE is able to reproduce the major features of the geographical patterns, seasonal cycle, and vertical distributions of the basic aerosol parameters. In particular, the model performs well under polluted continental conditions in the northern hemispheric lower and middle troposphere.Correspondence to: A. Lauer (axel.lauer@dlr.de) However, in comparatively clean remote areas, e.g. in the upper troposphere or in the southern hemispheric marine boundary layer, the current model version tends to underestimate particle number concentrations.

Abstract. We developed a global inventory for black carbon (BC) emissions from road traffic for 1993. Global emissions of 2.4 TgC were found in this year. The inventory was implemented in the atmosphere general circulation model ECHAM4.L39(DLR), together with inventories for BC emissions from fossil fuel combustion, biomass burning, and air traffic. The transport of BC particles and the concentration changes due to these emissions were investigated. Particularly, we focused on the contributions of road traffic emissions from North America, Europe, and Asia to the atmospheric BC burden. The sink of BC was parameterized as an exponential decay process with a half-lifetime depending on altitude. Because of the simplified BC cycle, the current investigation should be regarded as a pilot study. However, it is the first study dealing specifically with global road traffic BC emissions. The model results indicate that less than 20% of the BC mass concentrations predicted to be in the planetary boundary layer of the northern midlatitudes arise from road traffic. The road traffic fraction of BC concentrations over North America, Europe, and Asia originated mostly from emissions in the respective region. However, road traffic BC particles from Asia also significantly influence the tropopause region. In July their relative contribution is about 10%. A very rough estimate of the globally averaged direct radiative forcing of BC particles from global and Asian road traffic is given. As road traffic and its emissions in Asia are expected to rise in the near future, their relative importance will also grow and may, eventually, become a significant factor in anthropogenic climate change, unless the specific emissions are drastically reduced.