Case study of the ABL height and optical parameters of the atmospheric aerosols over Sofia

A study of the atmospheric boundary layer (ABL) height and its relation to the variations in the aerosol optical depth (AOD), Ångström coefficients, water vapor column (WVC) and total ozone column (TOC) was carried out in June 2011 and June 2012 at three sites in the city of Sofia (Institute of Electronics, Astronomical Observatory in the Borisova Gradina Park and National Institute of Geophysics, Geodesy and Geography). A ceilometer CHM15k, a sun photometer Microtops II, an ozonometer Microtops II and an automatic meteorological station were used during the experiments. Measurements of the AOD, WVC and TOC were done during the development of the ABL (followed by the ceilometer). In order to access microphysical properties of the aerosols, the Ångström coefficients α and β were retrieved from the spectral AOD data by the Volz method from three wavelength pairs 500/1020nm, 500/675nm and 380/1020nm. Comparison was done between the results obtained. Daily behavior of the AOD, Ångström exponent α and turbidity coefficient β, WVC and TOC are presented. Different types of AOD and WVC behavior were observed. The AOD had maximum values 1-2 h before ABL to reach its maximum height for the day. No significant correlation is found between TOC daily behavior and that of the AOD and WVC.