STATISTICAL METHODOLOGY Area valorization model estimates the capacity of the ecosystem to sustain certain level of concentration. The risk to ecosystems was evaluated through an standardized sten value, which estimated a region's sensitivity to pollution based on UN-ECE guideline values for mean-annual critical levels of SO2. The critical levels is defined as "the concentrations of pollutants in the atmosphere above which direct adverse effects on receptor such as plants, ecosystems or materials, may occur according to present knowledge". The sten (standard ten) scale was introduced within psychometry i,e. a branch of psychology dedicated to the methodology of the psychological measurement (tests, questionnaires etc.). Sten scale, like any other standardized scale, allows making the so-called norms of a given psychological test (variable, factor, dimension etc.) for a population the test is aimed. The scale, like many other standard scales, is based on the normal (statistical) distribution. This distribution is divided in 10 parts, which also are called stens. The mean (expectation, average) of the observed (non-standardized) value - roughly speaking - corresponds to the common limit: Upper limit of the 5-th sten Lower limit of the 6-th sten. From other point of view one can say that the expectation of stens is equal to 5.5. The length of each sten, excluding the two extreme, is equal to the half of the standard deviation. That has the following interpretation within our application: Once the SO2 concentration in the atmosphere grows 0.35 on the logarithmic scale, standardized scores should grow roughly 2 stens. We made some changes in the definition of the sten scale. The proposed changes take into account several differences that exist between psychological measurement and the standardization of the actual concentration of SO2 in atmosphere to the structure of land-cover of a given grid element. First of all our stens correspond linearly to the logarithms of the original scale. Two other changes reflect the fact that interpretation of a certain difference between two low concentrations has less significance within ecology than the same difference if we are beyond the critical levels that correspond to a given grid element. We defined also 11-th sten (the highest), which reflects the highest part of the lognormal distribution of SO2 concentration in atmosphere i.e. that part, which is above the 99.8 percentile limit. That limit can be crossed for a 30-minute period only. All these episodes can last less than 1 day yearly. There are several statistical procedures that operate on the sten data. One can check if the series of the SO2 concentration measurements has statistically higher value than given sten. This latter procedure is based on mean and standard deviation calculated from logarithms of a given series of measurements of SO2 concentration. Another procedure can be applied for stens and/or logarithms only. This procedure assesses if two series of concentrations differ significantly. Third statistical procedure gives indication if there is an alarm concentration in a given grid element. Such an indication is very useful to establish a radical change in the SO2 emission.