Acid deposition of substances is one of the most serious environmental problems in the Stockholm region. Even though the deposition of sulphur and nitrogen is lower than in many other European countries the soil and water in the north is more sensitive to this form of pollution.The Stockholm County Administration has commissioned SLB·analys to analyse the acid deposition by regional modelling of dry and wet deposition of sulphur and nitrogen in the Stockholm County.

Methods

Deposition models have been developed especially for the simulations in Stockholm County and are a part of the Stockholm Air Quality Management system. The total deposition of nitrogen and sulphur has been calculated for the hydrological year October 1994 to September 1995. The calculations are compared with measurements during the same period.

For model calculations of dry deposition of sulphur and nitrogen the AIRVIRO Grid Deposition model has been used. The concentrations of sulphur and nitrogen substances were calculated in 4x4 kilometers grids in the whole county.

Hourly meteorological data from the SLB·analys regional meteorological network were input to the dry deposition calculations. The hourly values for dry deposition were then accumulated to monthly and yearly values.

Emission input to the calculations of dry deposition were emission data from a detailed regional emission database.

The figure below illustrate the transport processes involved in the dry deposition of air pollutant gases and particles. The resistances are calculated from meteorological measurements and land-use data.