Columnar optical characteristics and radiative properties of aerosols of the AERONET site in Minsk, Belarus

Abstract

This study investigates columnar optical, microphysical and radiative properties of aerosols retrieved from the ground-based Aerosol Robotic Network (AERONET) station located in Minsk, Belarus. Mean values of aerosol optical depth (AOD), a measure of the amount of incoming light that aerosols prevent from reaching the surface, at a wavelength of 440 nm (AOD440) and Ångström exponent at 440–870 (AE440-870) between April 2002 and December 2019 were 0.22 ± 0.17 and 1.42 ± 0.29. A gradual decline of AOD440 by −0.009 and increase of AE440-870 by +0.0009 per year was noted. Seasonal change of AOD440 (AE440-870) demonstrates the highest values are in spring to summer and the lowest values are in winter for both indices. The data showed that the atmosphere over Minsk is under impact of various aerosol types with dominance of Continental Clean (СС) (52.21%), Mixed (MX) (24.30%) and Biomass burning/Urban-industrial (BUI) (20.54%) aerosol types, accounting for 97.05% of all aerosols. Aerosol volume size distribution (VSD), that defines the volume of all aerosol particles in the vertical atmosphere column, demonstrates a bimodal structure with clearly identified fine and coarse particles centered within a radius of 0.11–0.19 μm and 3.86–5.06 μm. Analysis of Asymmetry (ASY) parameter, Single scattering albedo (SSA), and Real and Imaginary Refractive Index (RRI and IRI) indicate the predominance of coarse-mode particles in autumn and winter; and fine-mode particles in spring and summer. The averaged aerosol direct radiative forcing (ARF) showed a cooling effect at the surface (SRF) and a significant warming in the atmosphere (ATM). The atmospheric heating rates varied from 0.40 ± 0.21 K day−1 (autumn) to 0.64 ± 0.38 K day−1 (winter). The results indicate definite changes in the aerosol optical, physical properties and types over Minsk during the study period.