Lidar observations of aerosol loadings extended throughout the troposphere

Durable aerosol/dust loadings affecting the atmosphere over the city of Sofia, Bulgaria (42.65 N, 23.38 E) were monitored by a Nd:YAG-laser-based lidar, from April to July 2009. The events lasted almost throughout the entire period. This study is only focused on the experimental results obtained on 15 and 23 April, when extraordinary in altitude (up to 15 km) aerosol layers were detected. For the two days, Dust Regional Atmospheric Model, provided by the Barcelona Super-Computing Center, had forecast Saharan dust incursions over Bulgaria. The origin of the aerosol layers detected by the lidar was identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory model for calculations of the backward air-mass trajectories. The results of measurements are presented in terms of time-averaged vertical profiles of the atmospheric backscatter coefficient and color maps in height-time coordinates, which illustrate the aerosol-mass spatial distribution and its temporal evolution, within the stable layers registered. Retrieved profiles at the two lidar wavelengths (532 nm and 1064 nm) are used to calculate the corresponding profiles of the backscatter-related Ǻngström exponent as a qualitative indicator of the dominant aerosol particle size fractions in the layers observed.