Improving Air Quality Modelling by Assimilation of Remotely Sensed Data

A contribution to ACCENT-TROPOSAT-2, Task Group 2

Martin Hvidberg

Dept. of Atmospheric Environment, National Environmental Research Institute
Ministry of Environment, Frederiksborgvej 399, Box 358, Denmark
Tel.:  (+45) 4630 1155
Fax:  (+45) 4630 1914

National Environmental Research Institute (NERI) operates an air pollution forecast model THOR. See these links respectively:,

THOR is known as a reliable forecast and assessment system for describing the spatial patterns in meteorology and air pollution over Europe. A possibility to assimilate validated remote sensing data into the THOR model would undoubtedly improve the ability of the model to accurately forecast Northern Hemisphere Air Pollution. The THOR model presently forecast the atmospheric constituent: NO, NO2, O3, SO2, SO4, HCHO, CH4, CO, Aerosols, H2O and HNO3. While BrO will be included later, for Hg modelling purposes.

THOR presently run a three-day forecast, every six hours. The model domain is the EMEP grid of the Northern Hemisphere. This 50 km by 50 km grid is subdivided in 3 by 3 sub-cells over Europe, providing a 16.6 km by 16.6 km model grid. The model is also used locally, in yet denser grids, to access concentrations of atmospheric constituents for input to various other models including assessments of pollution pressure on human health.

The aim of assimilating remotely sensed data into the THOR model is twofold. To improve the accuracy and reliability of the forecasts and assessments, benefiting not least persons with air ways diseases. And secondly, not but less important, to improve our understanding of the physical and chemical processes in the atmosphere.

The operational version of the THOR system includes assimilation of data from a number of ground measurement stations. Further inclusion of truly spatially distributed data from remote sensing would enable us to improve the accuracy and reliability of the system, especially in areas distant to ground measuring stations.

Specifically the THOR development team hopes to find improvements in the description of the O3 and NO2 concentrations by including data from GOME or SCIAMACHY, especially if data are available to support a 3-D O3 description. In a longer perspective the preparations of ACE+ measurements of temperature and humidity are regarded as highly relevant.

Since THOR is based on, and validated against, ground station measurements it could serve AT2 with spatially distributed ground-truth values. These might be useful as validation of remote sensing data and procedures. Although the AT2 remote sensing products are already benefiting from calibration, this is commonly based on point measurements. THOR provides a complete cover (EMEP grid) data set with a number of parameters to be directly compared with remote sensing derived information. The THOR development group would be honoured to provide these data to ACCENT/AT2.

The presently proposed project supports the ACCENT objectives by providing contact to, and collaboration with an already recognised research group within atmospheric and air pollution science.


J.Brandt, J. Christensen and L.M. Frohn


The initialisation of the projects is dependent on further funding. Potential sources are: NMR - Nordic Council of Ministers, National Research Council, Denmark and the EU Danish Environmental Protection Agency


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