Summary

The inverse modelling technique has been explored in a first approach using trajectories instead of a full dispersion model to derive a source-receptor matrix for sulfur emissions in Europe, based on a one-year data set from the EMEP monitoring network. A simple regularisation constraint without detailed a-priori knowledge was found to be sufficient to recover qualitatively the major sulfur emission areas in Europe. This method can be used as an alternative to trajectory statistics for source determination.

Some preliminary work has been done for the inverse modelling of the Chernobyl accident source term.

Aim of research

This contribution aims at the development of inverse modelling methods to derive information on emissions from measurements in the regional scale. Such methods shall be applied to suitable data sets and results be compared with conventional emission estimates. In addition, recommendations on the optimum monitoring network design shall be made.

Activities during the year

The preliminary work on using trajectories as a substitute for a full dispersion model to derive source-receptor relationships and the development of regularisation techniques for such data sets has been continued and completed for the time being.

In preparation for a test of the inverse modelling approach with the Chernobyl accident, the ATMES data set of radiological measurements (Klug et al., 1992) has been acquired from JRC Ispra, and the respective gridded precipitation analysis from KNMI. Furthermore, ECMWF reanalysis data (Gibson et al., 1997) for the period of the Chernobyl accident have been extracted from ECMWF's MARS data base in the format required for the planned application of the Lagrangian particle dispersion model FLEXPART (Stohl et al., 1998)

The principal investigator participated in the "Workshop on Inverse Methods in Global Biogeochemical Cycles" from 16 to 20 March 1998 in Iraklio, Greece. She presented a poster on inverse modelling of sulfur emissions in Europe based on trajectories. This paper has been submitted for publication in an AGU Geophysical Monograph volume with results of this workshop (Seibert, 1999).

From 2 to 4 November 1998, the principal investigator participated in the annual workshop of the EUROTRAC-2 subproject GENEMIS in Budapest, and gave an introductory presentation on inverse modelling.

Principal results

An inverse modelling study based on trajectories and daily measurements of airborne sulfate at 13 background stations in Europe during one year has been carried out. A source-receptor relationship matrix was calculated from the trajectories which were utilised as a first approximation to a full dispersion model. The matrix was inverted with simple constraints for regularisation (Neumaier, 1998). No detailed a-priori information was used, and instead the total length of the solution (emission vector) as well as its "roughness" (represented by the Laplacian of the emission field, weighted with a function depending on the trajectory density) was minimised. This worked well enough to reproduce major emission areas in Europe (black triangle, England, Northern Italy, Kola peninsula) in a qualitative way. However, the dynamic range of the emission values was severely underestimated. This method can serve as an alternative to conventional trajectory statistics (Seibert et al., 1994; Seibert and Jost, 1994; Stohl, 1996) as well as a first step towards inverse modelling based on full dispersion models.

Aim for the coming year

The FLEXPART model shall be applied to the ATMES Chernobyl data set to produce a source-receptor matrix, where the source term is divided into time and release-height slots, to invert this matrix and apply it to the radioactivity monitoring data in order to retrieve the source strengths which will be compared with conventional estimates. We shall also see whether we can use the FLEXPART model in backward (adjoint) mode.

The IMPO Lagrangian box chemistry and transport model (Wotawa et al., 1998), which is already designed for backward (receptor-oriented) mode shall be adapted for the production of source-receptor matrices, especially with respect to sulfur compounds. Then it shall be used for inverse modelling of the sulfur emissions in Europe and possible other data sets. Alternatively, the FLEXPART model could be used in backward mode, however, this would mean that chemistry can not be considered.

Acknowledgements

The funding of the Austrian "Fonds zur Förderung der wissenschaftlichen Forschung (FWF)" under grant P1295-GEO is gratefully acknowledged. We thank ECMWF, ZAMG, EMEP MSC-W, FMI and A. Stohl (University of Munich) for meteorological and air quality data as well as trajectories.

References

Gibson, J.K., P. Kallberg, S. Uppsala, A. Hernandez, A. Nomura and E. Serrano; ERA Description. ERA Project Report Series, No. 1. European Centre for Medium-Range Weather Forecasts, Reading, UK (1997). [back to text]

Klug, W., G. Graziani, G. Grippa, D. Pierce and C. Tassone (eds.); Evaluation of long range atmospheric transport models using environmental radioactivity data from the Chernobyl accident. The ATMES report. Elsevier, London (1992), 366 pp. [back to text]

Neumaier, A.; Solving ill-conditioned and singular linear systems: A tutorial on regularization. SIAM Review 40 (1998), 636-666. [back to text]

Seibert, P. and D.T. Jost; Investigation of potential source areas by statistical trajectory analysis of ALPTRAC aerosol measurements. EUROTRAC-Newsletter 14 (1994), 14-17. [back to text]

Seibert, P., H. Kromp-Kolb, U. Baltensperger, D. T. Jost, M. Schwikowski, A. Kasper and H. Puxbaum; Trajectory Analysis of Aerosol Measurements at High Alpine Sites. In: P.M. Borrell, P. Borrell, T. Cvitas, W. Seiler (eds.), Proc. EUROTRAC Symposium '94, SPB Academic Publishing bv, The Hague (1994), 689-693. [back to text]

Seibert, P.; Inverse modelling of sulfur emissions in Europe based on trajectories. Submitted for Inverse Methods in Global Biogeochemical Cycles (AGU Geophysical Monograph, eds. P. Kasibhatla, M. Heimann, D. Hartley) (1999) [back to text]

Stohl, A.; Trajectory statistics - A new method to establish source-receptor relationships of air pollutants and its application to the transport of particulate sulphate in Europe. Atmos. Environ. 30 (1996), 579-587. [back to text]

Stohl, A., M. Hittenberger and G. Wotawa; Validation of the Lagrangian particle model FLEXPART against large-scale tracer experiment data. Atmos. Environ. 32 (1998), 4225-4264. [back to text]

Wotawa, G., A. Stohl and B. Neininger; The urban plume of Vienna: Comparison between aircraft measurements and photochemical model results. Atmos. Environ. 32 (1998), 2479-2489. [back to text]

[BOKU] [IMP] [Inverse modelling main page] [ Top of page ]

Last update: 14 Jan 1999 by P. Seibert | URL of this page: http://www.boku.ac.at/imp/envmet/et2-annrep98.html