Lennart Robertson

An Eulerian Limited-Area Atmospheric Transport Model

Abstract A limited-area, offline, Eulerian atmospheric transport model has been developed. The model is based on a terrain-following vertical coordinate and a mass-conserving, positive definite advection scheme with small phase and amplitude errors. The objective has been to develop a flexible, all-purpose offline model. The model includes modules for emission input, vertical turbulent diffusion, and deposition processes. The model can handle an arbitrary number of chemical components and provides a framework for inclusion of modules describing physical and chemical transformation processes between different components. Idealized test cases, as well as simulations of the atmospheric distribution of 222Rn, demonstrate the ability of the model to meet the requirements of mass conservation and positiveness and to produce realistic simulations of a simple atmospheric tracer.

Source function estimate by means of variational data assimilation applied to the ETEX-I tracer experiment

The ETEX data set opens new possibilities to develop data assimilation procedures in the area of long-range transport. This paper illustrates the possibilities using a variational approach, where the source term for ETEX-I was reconstructed. The MATCH model (Robertson et al., 1996) has been the basis for this attempt. The timing of the derived emission rates are in accordance with the time period for the ETEX-I release, and a cross validation, with observations beyond the selected assimilation period, shows that the source term gained holds for the entire ETEX-I experiment. A poor-man variational approach was shown to perform nearly as good as a fully variational data assimilation. The issue of quality control has not been considered in this attempt but will be an important part that has to be addressed in future work.

Validation of the operational emergency response model at the Swedish Meteorological and Hydrological Institute using data from ETEX and the Chernobyl accident

Abstract The Eulerian atmospheric tracer transport model MATCH (Multiscale Atmospheric Transport and Chemistry model) has been extended with a Lagrangian particle model treating the initial dispersion of pollutants from point sources. The model has been implemented at the Swedish Meteorological and Hydrological Institute in an emergency response system for nuclear accidents and can be activated on short notice to provide forecast concentration and deposition fields. The model has been used to simulate the transport of the inert tracer released during the ETEX experiment and the transport and deposition of 137Cs from the Chernobyl accident. Visual inspection of the results as well as statistical analysis shows that the extent, time of arrival and duration of the tracer cloud, is in good agreement with the observations for both cases, with a tendency towards over-prediction for the first ETEX release. For the Chernobyl case the simulated deposition pattern over Scandinavia and over Europe as a whole agrees with observations when observed precipitation is used in the simulation. When model calculated precipitation is used, the quality of the simulation is reduced significantly and the model fails to predict major features of the observed deposition field.

Concentration and deposition of acidifying air pollutants over Sweden: Estimates for 1991 based on the match model and observations

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. MATCH is an Eulerian atmospheric dispersion model, including physical and chemical processes governing sources, atmospheric transport and sinks of oxidized sulfur and oxidized and reduced nitrogen. Using a combination of air and precipitation chemistry measurements and the MATCH model, the national and long-range transport contributions to air pollution and deposition can be quantified in the model region. The calculations for the year 1991 show that the Swedish import was about 4.5 times larger than the export for sulfur and about six times larger for reduced nitrogen, while the Swedish import of oxidized nitrogen only exceeded the export by 10%. Using the MATCH system we estimate the long-range transport in an independent way compared to EMEP. Comparison between the EMEP and MATCH calculations for 1991 show that the total deposition of oxidized nitrogen over Sweden is similar, while the EMEP-values for total deposition of oxidized sulfur and reduced nitrogen are 25% respectively 40% smaller than what is obtained from MATCH.

Modelling of sulfur deposition in the southern Asian region

Acidification problems in developing countries are expected to become more prevalent in the coming decades. Assessments of means of abatement strategies are likely to become of vital interest. This paper presents some preliminary results of modelling of acidic deposition due to anthropogenic emissions of sulfur in the Southern Asian region. It is concluded that the study has some shortcomings, that has to be addressed in future work, such as lack of treatment of deep convection and that deposition and transformation rates used are not adapted to the tropics. Only very limited validation has been possible due to the lack of relevant measurements. Wet deposition data from rural Thailand are in fair agreement with calculated values. The study is one part of a larger project encompassing mapping ecosystem sensitivity to acid deposition, wet chemistry measurements and atmospheric transfer modelling.

Evaluation of new model tools for meeting the targets of the EU Air Quality Directive: a case study on the studded tyre use in Sweden

Two new model tools have been developed for meeting the EU Air Quality Directive targets: SIMAIRroad (related to traffic emissions) and SIMAIRrwc (rwc standing for residential wood combustion). The models have been evaluated for different traffic situations and for residential areas with wood combustion, with promising results. The models can calculate PM10 statistics, such as mean values and 90 and 98 percentiles, that are well within ±50%. In fact, most of the results are within ±25%. Studded tyres are one important factor causing high PM10 concentrations in Swedish streets, so reducing their use would considerably improve air quality.

Air Pollution Assessment Studies for Sweden Based on the Match Model and Air Pollution Measurements

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. Model versions covering Europe, Sweden and subregions of Sweden have been used as a basis for decision making concerning environmental protection in Sweden. MATCH is an Eulerian atmospheric dispersion model, including physical and chemical processes governing sources, atmospheric transport and sinks of oxidized sulfur and oxidized and reduced nitrogen. With the MATCH system, air pollution contributions from different source types like traffic, industry, shipping, farming etc. can be obtained. Using a combination of air and precipitation chemistry measurements and the MATCH model, the contribution of air pollution and deposition from long-range transport can be quantified in the model region. Also hourly mappings of ozone concentrations are obtained. The calculations for the year 1991 show that the Swedish import was about 4.5 times larger than the export for sulfur and about six times larger for reduced nitrogen, while the Swedish import of oxidized nitrogen only exceeded the export by 10%. Using the MATCH system we estimate the long-range transport in an independent way compared to EMEP. Comparison between the EMEP and MATCH calculations for 1991 show that the total deposition of oxidized nitrogen over Sweden is similar, while the EMEP-values for total deposition of oxidized sulfur and reduced nitrogen are 25% respectively 40% smaller than what is obtained from MATCH. The Swedish contributions to deposition over Sweden are also somewhat smaller (20–38%) in the EMEP model compared to MATCH. Results from MATCH for the year 1994 show a decrease in sulfur deposition over most of Sweden, both from Swedish sources and long-range transport, except for south-east Sweden where a pronounced increase in long-range transport contribution was obtained.

On The Issue Of Quality Control In Data Assimilation

Attempts to use ETEX-I data to reconstruct the source term of the experiment has been shown to be rather successful by means of variational data assimilation using the Eulerian transport model MATCH (Robertson and Langner, 1998). We have taken one step further and investigated the possibilities of quality control of data within the concept of variational data assimilation. With the adopted strategy it is found that the quality control mainly skip zero observed values, that does not agree with the model. To some extent is this justified by the representative error in the measurements in relation to the scale over which the model is valid. So far we have not gained anything but experience from this quality control approach. The quality control does not improve the model performance which never the less encourage us to further investigate the use of quality control.

Match: A Mesoscale Atmospheric Dispersion Model and Its Application to Air Pollution Assessments in Sweden

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. It has been used as a basis for decision making concerning environmental protection within Sweden or subregions of Sweden.

On the Application of Four Dimensional Data Assimilation of Air Pollution Data Using the Ajoint Technique

Feedback mechanisms of air pollution data into dispersion models are of interest in e.g. emergency response systems dealing with hazardous releases. On the local scale Goavaerts and Sohier (1989) among others have suggested algorithms focusing on the input parameters. On the regional scale, though, little has been done in terms of air pollution data. However, looking into other areas as e.g. numerical weather forecasting or oceanographic modelling extensive work has been undertaken for some decades, (see e.g. Gandin (1963), Lorenc (1986)). The feedback process in this field is normally denoted data assimilation.