Investigation of the atmospheric boundary layer and optical characteristics of the atmospheric aerosols over Sofia in summer 2016

Observations of the aerosols vertical distribution and an assessment of their optical properties on clear sunny days and days with Saharan dust intrusions were carried out in the summer of 2016 in the mountain valley of Sofia, Bulgaria. In this paper, some of the results obtained during Saharan dust intrusions are presented. Measurements were carried out with active and passive remote sensing devices as well as with in-situ ones. A ceilometer CHM-15k, a sun photometer Microtops II, an ozonometer Microtops II and a laser particle counter (LPC) PC 200 were used. The atmospheric boundary layer (ABL) height was determined from the high temporal and spatial resolution ceilometer data and from aerological sounding. The changes in fine particle concentration in space and time were measured by the six-channel LPC located in the Borisova Gradina Park, Sofia. HYSPLIT back trajectory model and the BSC-DREAM dust model were used as additional source of information for selected days. The observed ABL height varied from 200 to 2500 m for the presented experimental days. During the campaign, the aerosol optical depth (AOD) at wavelength λ = 380 nm ranged from 0.30 to 0.56, at λ = 500nm - from 0.18 to 0.30 and at λ = 1020 nm - from 0.01 to 0.10. The water vapor content (WVC) changed between 1.5 cm and 2.1 cm. The total ozone content (TOC) varied from 225 DU to 275 DU.