Influence of air temperature inversions on the air pollution dispersion conditions in Krakow

Krakow is one of the most polluted cities in Poland. Its natural ventilation is limited due to the location of the city in a river valley. Air temperature inversions are an important element of the local climate in Krakow and a factor strongly influencing air pollution dispersion conditions. Traditional, multi-annual (1972-1996) measurements of air temperature, from three rural stations, and 1-year (03.2009-02.2010) intensive automatic measurements from two rural stations, one urban station and from a mast top 115 m above the ground were used. In the night time, inversions are less frequent in the urban than in the rural area, but still the frequency is over 30% from spring till autumn. In the studied 100-meter air stratum, no crossover effect was found. The relatively high frequency of air temperature inversions in the urban area of Krakow is a significant mesoclimatic difference in comparison with cities located in flat areas. It is also a factor seriously decreasing the natural ventilation and air pollution dispersion conditions.