The influence of thermal inversions on the variability of sulphur dioxide concentrations in calendar winter (December to February) was assessed based on a 10-year measurement series from 2004/2005 to 2013/2014. The data on daily sulphur dioxide concentrations were obtained from four urban air quality measurement stations operated in a measurement network by the Regional Inspectorate of Environmental Protection (WIOŚ) in Wrocław, and from the ARMAAG Foundation in Gdańsk. The occurrence of thermal inversions was traced based on data from aerological measurements conducted twice daily (at 00:00 and 12.00 UTC) at two aerological stations, in Wrocław and in Łeba. This allowed us to determine the thickness of the surface (lower) inversion layers, as well as the height of the base and thickness of the first (the lowest) layer in the free atmosphere (upper). The effect of inversion on the variability of daily SO2 concentrations was investigated using single linear regression at statistical significance levels of α = 0.05 and α = 0.01. The conditions promoting dispersion of pollutants in the lower troposphere in the winter seasons from 2004/2005 to 2013/2014 depended predominantly on the upper inversion layers, which occurred in both regions at comparable frequency of almost 90%, both in daytime and nighttime. Surface inversions were recorded significantly less frequently, mostly at night. The data also showed that the thickness of inversion layers and the height at which they formed affected the concentration of SO2, although the statistically significant role of upper inversions manifested itself at both times of the 24-hour period, whereas the role of surface inversions was evident only at night.

22.4.2016