Influence of morphology on the ventilation of polluted areas – a case study from Rybnik Plateau, Poland

In the present study an attempt was made to determine the degree of effective ventilation of the valleys in the area of the Rybnik Plateau, based on the example of the environs of Jastrzębie Zdrój, a city with high air pollution. For the analysis of the conditions of airing of valleys the areas with different physico-geographical characteristics, primarily in terms of density of the valley network, origin and morphology of the valleys, and type of surface deposits were selected. 49 cross-valley profiles were drawn for the selected valleys; on the basis of the profiles the following parameters were calculated: the distances between the edges of each valley, valley bottom width, and depth of the valleys. The degree of ventilation of each valley was calculated after the formulae of Kaps (1955) and Błażejczyk (1975). The lowest values of the index of effective ventilation were recorded almost in all main loessial valleys in the southern part of the area. This indicates their weak or even extremely weak degree of ventilation. The valleys in the remaining area, open predominantly to N and E, are most commonly aired to a sufficient degree. This is determined by their morphology, especially smaller depth, smaller relative heights and higher mean wind speed. The example presented in this study shows that the index of effective ventilation, even if it is calculated for a relatively small area, reflects the characteristics of the local environment extremely well which is relevant from the perspective of the movement of contaminated air.