Status Reports

Scientific achievements during the last 15 months:

During the last 15 months of PHOENICS project the proposed work in all workpackages has been fully accomplished.

In addition to the initially proposed work in WP1 that has been completed during the second year of the project, novel observational organic aerosol measurements in marine environment became available. These data prove the existence of an organic aerosol marine source.

M7/EQSAM has been further improved to consider crustal components and small molecular weight organic acids. The new thermodynamical/dynamical aerosol model M7/EQSAM has been implemented into the climate model ECHAM5, fully coupled with various emissions, deposition processes and the gas phase chemistry. The pre-operational model is able to simulate well inorganic aerosol and visibility variability in polluted regions

To simplify the calculation of aerosol water associated with organic aerosol, a parameterisation of water activity of aerosol hygroscopic organic species has been developed based on observational data. The variability of the Secondary Organic Aerosol (SOA) burdens formed from natural emissions during the last decades has been evaluated to be of the same order of magnitude as the SOA formed from anthropogenic emissions. SOA contributes by 3 % to the European AOD. A review paper on OA and climate modelling, with contributions from 22 authors, has been published as an outcome of the PHOENICS workshop on OA organised in Sept. 2003.

We developed a parameterisation describing the physico-chemical coupling of gas-phase chemistry-aerosol and cloud droplets, with a focus on the formation of sulphate by in-cloud oxidation of SO2. The development of this cloud processing parameterization was concluded with the implementation in the aerosol-climate model ECHAM5/HAM. The parameterization estimates the cloud drop number concentration from the simulated aerosol characteristics (aerosol number concentration, average particle size, size standard distribution and chemical composition) and the vertical velocity in large scale clouds, and then simulates the aqueous phase formation of sulphate within each activated aerosol mode, with realistic results. We investigated the sensitivity of the spatial distribution of aerosol sulphate and the cloud drop number concentration to the parameterisation. It was found that the sulphate aerosol distribution was not affected significantly by the details of the cloud processing treatment, however the cloud drop number concentration was more sensitive. It was concluded that estimation of the aerosol direct effect, main focus of PHOENICS, does not critically depend on the calculation of in-cloud sulphate formation.

The improved precipitation scavenging and dry deposition parameterisations were employed in the ECHAM5/HAM PHOENICS base runs. The sensitivity tests with the aerosol module implemented in the cloud model WRF (Weather Research and Forecast model) were extended, examining the relative roles, compensating abilities, and importance of uncertainties for the various scavenging pathways for different aerosol size classes. The two key parameters for aerosol scavenging, water vapour and precipitation distributions, were evaluated using satellite based observations, showing the overall good quality of the ECHAM5 simulation, pointing towards specific biases which are being examined further, and uncovering the critical role of the evaporation of convective precipitation for determining lower tropospheric water vapour amounts and lifetimes.

The development of the global model TM5 with a high resolution two way nested zoom over Europe has been finalized. TM5 contains a coupled aerosol-photochemistry description. Results of TM5 and of several other PHOENICS models have been employed to calculate the European aerosol distribution. The LOA-LMDZ and ECHAM GCMs have been used to calculate the contribution of European anthropogenic aerosol sources to the direct effect. The off-line CTM TM5 was used to estimate uncertainties in the aerosol budget associated to the emission inventories of aerosol precursors, the model resolution, and the wet removal parameterization. The output of the models has been consistently evaluated within the international AEROCOM aerosol module inter-comparison exercise.

We developed a new parameterisation of the optical properties of the mixed aerosol and the compared model results to remotely sensed observations to minimize and evaluate uncertainties relevant to the direct climate effect of aerosols. For the first time, the aerosol radiative impact has been estimated systematically for each component not only in the shortwave but also in the longwave spectrum. The state-of-the-art MODIS aerosol retrievals combined with TOMS and SSM/I measurements have been used within PHOENICS to estimate the clear-sky direct radiative forcing for the year 2002. For the first time, aerosol direct radiative forcing can be estimated by aerosol type both over ocean and land from observations only.

Parameterizations on size-resolved formation, removal and abundance of aerosols and associated water, have been evaluated coupled with the A-GCM ECHAM5. 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. The response of global aerosol system to changes in anthropogenic emissions has been analysed and deviations form additivity have been demonstrated. Comparison of AOD model calculations with remote sensing ground based and satellite measurements showed an excellent agreement.

The model results from the PHOENICS aerosol models (TM5, ECHAM, LMDzT-LOA and LMDzT-INCA) have been assembled and analysed together with those from 12 other global aerosol models (obtained in the frame of the AeroCom initiative). A systematic comparison to surface aerosol observations, to sun photometer measurements; lidars and satellite derived optical depth products has been finalised and is accessible across a public web interface. The PHOENICS models perform excellent with respect to the majority of the AEROCOM models. Inter-annual and seasonal variability is shown to be less important than inter-model differences in representing the aerosol dynamics. The budget analysis in the different aerosol models documents the diversity of current aerosol parameterisations especially with respect to natural aerosols, hygroscopicity and conversion from emission to optical properties. Dedicated model simulations from an ensemble of AEROCOM aerosol models for present and pre-industrial conditions reveal that 25% of the aerosol optical depth is anthropogenic. The resulting direct forcing estimate from an ensemble of models is suggested to be more robust than those from individual models.

Conclusions:


PHOENICS has been successfully met the objectives set at the beginning of the project. PHOENICS developed a host of parameterisations of aerosol formation, and removal processes, which were evaluated by comparison of model results with observations collected and harmonized within the framework of PHOENICS. The current direct aerosol effects have been derived both by A-GCM modelling coupled with the aerosol dynamic module and by satellite observations.

The aerosol direct effect in the longwave has been calculated for the first time and was found to be minor compared with shortwave aerosol forcing. Anthropogenic aerosols increase the outgoing shortwave flux by 2.7 Wm-2 at the top of the atmosphere, in clear-sky on a global, annual average.

PHOENICS models estimate modest direct anthropogenic aerosol radiative forcing of -0.15 to -0.3 Wm-2 at the top of the atmosphere in all-sky on a global, annual average.

The contribution of European anthropogenic emissions to AOD over Europe has been estimated by 3 different PHOENICS models to be 40-50% of the total AOD. Implementation of currently planned emission reductions of aerosol and aerosol precursor gasses indicate a larger future role of aerosol nitrate in Europe.