This article presents the results of a study related to variations in aerosol optical depth, total ozone content, water vapor content and angstrom coefficients from three experimental campaigns carried out in June 2010, June 2011and 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 (NIGGG)). A ceilometer CHM15k, two sun photometers Microtops II and an automatic meteorological station were used during the experiments.

The height of the mixing layer varied from 1500m to 2500 (3000)m during the measurements. The height of the residual layer ranged from 800m to 2000m. The stable boundary layer extended to 200-400m over the campaigns.

The aerosol optical depth (AOD) at wavelength λ = 500nm ranged from 0.38 to 0.66 in the first campaign and from 0.24 to 0.55 in the second one and from 0.11 to 0.23 in the third one. Corresponding ranges for the water vapor content (WVC) were 1.26cm to 2.6cm. Different types of aerosol optical depth and water vapor content behavior were observed. Additional resource of information about the origin of the aerosol layers detected by the ceilometer CHM15k offered the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model. The calculations of backward air mass trajectories give a plot of the road that the air mass traversed for a chosen time period before to arrive to the location of Sofia city.

The total ozone content (TOC) varied from 240 DU to 370 DU during the campaigns. The ground - based observation from ozonemeter Microtops II with satellite observation of Ozone Monitor Instruments (OMI) over Sofia (Bulgaria) are compared. Our results have implications for the further study of regional climate variability.