A Wintertime Local-to-Regional Scale Test Case Study of SILAM Model

The SILAM model (version 4.5.4) is applied for retrospective modelling of wintertime deposition fluxes of fly ash and sulphate near Estonian oil-shale-based industrial complex. The fluxes are validated against snow-based deposition measurements that have been carried out during nine winters since 1985. Also, the data from the Lahemaa (Estonia) and Virolahti (Finland) EMEP stations are applied for regional-scale validation. In this test case SILAM tends to systematically underestimate the deposition of fly ash and overestimate the deposition of sulphate at distances up to 30 km from the pollution sources. Overestimation of sulphate is severe during recent decade, whereas at more remote (100 km) EMEP stations the fluxes are nearly correct. As SILAM is basically developed and validated for meso-scale applications, some scale-dependent effects near the sources may appear. The recent changes in oil shale combustion technology may also play a role in increasing overestimation trend for sulphate.