Regional Source Quantification model for sulphur oxides in Europe

Abstract An air quality model for estimation of emissions on a regional scale is developed. The model uses measured air concentrations and air trajectory transport calculations to determine the emissions. The optimal emission strength is obtained by a least square approximation between measured and estimated air concentrations of pollutants. The Regional Source Quantification (RSQ) model is used on the European Long-Range Transport data base for sulphur oxides collected by the Norwegian Institute for Air Research. The data base consists of about 60,000 SO 2 and SO 4 air quality samples and four times as many 48-h back trajectories. The estimated emission strengths based on about 7500 samples are shown to agree fairly well with the national emission strengths estimated previously from population and industrial density as well as consumption of fuel and raw materials. This is taken as a verification of the RSQ model. Use of the RSQ model in future studies for estimating emissions of other micropollutants is discussed. Optimal location of monitoring stations and emission fields as well as the duration of the study period are related to the standard deviations on the emission strengths. The RSQ model is used not only for emission estimation but also for estimation of optimal decay and oxidation parameters to be used in the air trajectory model. We find the decay parameter for SO 2 to be 1.3 × 10 −5 s −1 , and for SO 4 to be 1.6 × 10 −6 s −1 . The emission plus initial oxidation to SO 4 is found to contain about 12% of the total sulphur emission, while the succeeding oxidation defined in the air trajectory model is found to be insignificant.