Status Reports

Scientific achievements during the 2nd year:

During the 2nd year of PHOENICS project progress was made in all workpackages of the projects, data compilation, process parameterization and global model development. A systematic compilation of data, both on aerosol composition and size distributions measured at the earth surface as well as hygroscopicity and optical properties. Data sets from satellite remote sensing and sun photometers have been analyzed and harmonized. The data became available on time to all partners for model evaluation purposes. LIDAR measurements that allow evaluation of the parameterisations of aerosol wash out have now become available.

Significant progress has been made on the development of the thermodynamic model EQSAM by including sea-salt and dust aerosol components and its coupling to M7. The coupling, however, raised non-trivial and fundamental questions, such as “What are the criteria which determine the fraction of soluble matter that might be transformed into insoluble matter due to the condensation of inorganic or organic acids (known as the ageing of aerosols). The application of the new dynamical and thermodynamical aerosol model M7/EQSAM within the new version of the climate model ECHAM5, fully coupled with various emissions, deposition processes and the gas phase chemistry has been a real challenge and is now under testing.

The developed parameterization SOA formation from anthropogenic and naturally emitted VOC has been used to identify the critical parameters of uncertainties in global SOA modeling. Preindustrial and Present day simulations of aerosol loading have been performed although the available kinetic data do not distinguish between high and low NOx environments. Comparison between the two simulations demonstrates that the percent contribution of the SOA to the total OA mass has globally decreased since preindustrial times although the absolute mass is almost an order of magnitude higher nowadays than under clean preindustrial conditions. The chemical composition of this SOA has been also modified due to humans. To attribute the appropriate hygroscopic properties to the SOA compounds lumped for global modelling purposes, a number of chamber experiments have been performed. They investigated the hygroscopic properties of the SOA formed during the a-pinene and toluene oxidation.

Simulations with a detailed cloud parcel microphysics model show that precipitation formation in warm clouds may respond highly non-linearly to changes in updraft speed and aerosol properties. This is relevant for the aerosol lifetime and thus for climate change associated with the changing aerosol abundance in the atmosphere. The results suggest that the parameterizations for drizzle formation in climate models do not adequately represent these non-linearities. Other simulations illustrate the need for these parameterizations to account explicitly for externally mixed aerosol in order to accurately predict CDNC.

The development and implementation of the size-resolving dry deposition scheme in ECHAM for use in the PHOENICS base runs has been completed. An initial version of the precipitation scavenging parameterisation in ECHAM has been finalised for use in the PHOENICS base runs. Sensitivity tests with the aerosol module implemented in the cloud model WRF (Weather Research and Forecast model) are performed to provide information for use in improving the precipitation scavenging parameterisation in ECHAM. Evaluation of key parameters for aerosol scavenging like water vapour and precipitation distributions are evaluated using satellite based observations.

The objective set out for the second year of the project to have available a working and tested version of the chemistry transport model TM5 at the end of year, has been reached. Indeed, the global 2-way nested zoom model TM5 has now been thoroughly tested and the building blocks of aerosol modelling tools have been implemented. Transport has been validated with 222Rn measurements at Finokalia (Crete) and the results clearly show the advantages of zooming for short-lived compounds. The first results using full chemistry coupled to a thermodynamic inorganic aerosol model show that the European EDGAR3.2 emissions for 1995 seem to be too high for a 2001 model simulation.

The parameterisation of the optical properties of the mixed aerosol and the comparison of model results to remotely sensed observations to minimize and evaluate uncertainties relevant to the direct climate effect of aerosols. For this, during the 2nd year of the project a module for aerosol optics suited for use with the M7 aerosol module within the project has been developed and made available to the partners. The uncertainties involved in the aerosol shortwave radiative forcing calculations have been investigated by the mean of 1-d studies. Since satellite provide observations at fixed local time and sunphotometers provide daytime observations only, the sensitivity of the aerosol optical depth to the diurnal cycle of biomass burning emission has been investigated and has been proven to be minor probably due to the relatively long lifetime of aerosols.

The parameterizations developed in WP 2, 3, 4, 5, 7 have been harmonized in the 1-D version of the A-GCM and interact with partners if needed for harmonization purpose. The combined effort of these parameterizations on size-resolved formation, removal and abundance of aerosols, taking into account uncertainties of parameterizations is under evaluation. 3-dimensional A-GCM simulations have been performed assimilating the observed meteorology for selected periods for comparison of the model results with observations obtained during intensive field campaigns. The direct effect of the aerosols on climate has been computed taking into account the number and mass distributions of the mixed aerosols.

A suite of interannual simulations with the LMDzT-INCA model has been performed for the years 1996 to 2002 when observational data are of best quality. Evaluation of the PHOENICS and AEROCOM simulations is part of the AEROCOM intercomparison exercise.

Uncertainty evaluation is also the major objective of the AEROCOM intercomparison exercise that is co-organised by PHOENICS. Thus the evaluation of the robustness of the calculations, initially planned for the PHOENICS models, has been now extended to the international community models. A few preliminary conclusions can be drawn from this exercise. GCM’s operating in a climatological mode have significantly less skill to reproduce observed variability. An averaged model (combining several model results) shows better correlation than individual models to observed satellite observations, therefore combining results from different models seem to reduce model errors. Interannual variability is a source of error when comparing to data. Inter-model differences seem to be more important than inter-annual variability.

Conclusions:

The systematic approach to determine the direct effect of the mixed and size-resolved aerosol considering all its major components is progressing according to the Description of Work document. The first climate effect calculations have been now undertaken in the frame of the project. The first parameterisation for use in the global models have been developed and evaluated by comparison with observations. The OA workshop organised by the project at mid-term has reviewed up-to-date knowledge on Organic aerosol and guided further development in the project. Both A-GCMs are operational now and the M7 aerosol module already coupled with ECHAM5 and EQSAM thermodynamic model is providing the first mixed aerosol chemical size-distribution results. An important effort is undertaken in the uncertainty estimate within all WP of the project but also in the frame of the AEROCOM intercomparison exercise that is co-organised by PHOENICS.