Spatial variation in wet deposition amounts of sulphate due to stochastic variations in precipitation amounts

The possibilities of estimating exact pollution deposition amounts are limited by several factors. For the wet deposition fraction of the deposition, one factor is the imperfect knowledge of precipitation amounts, which in turn is partly due to the stochastic character of precipitation. In this paper an attempt is made to estimate how large this inaccuracy in wet deposition may be. The area chosen for the study, Pohjanmaa in western Finland, is climatologically and topographically fairly homogeneous. The variation in precipitation amounts within this area is therefore mainly random by nature. According to the estimations made, there is a spatial variation in the annual wet deposition in the area studied of 5–20% due to stochastic variations in precipitation amounts. This result is in good agreement with the differences in annual deposition amounts for sulphate observed between three measurement stations located in the same area. Sulphate is used as the reference pollutant.