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

Highlights

• Long term continuous data on columnar optical, microphysical and radiative properties over Minsk.

• High AOD₄₄₀ (AE_440-870) in spring (summer) and the lowest values in winter for both indices.

• Continental Clean, Mixed and Biomass burning/Urban-industrial is the dominant aerosols types.

• Predominance of coarse-mode particles in winter and autumn; and fine-mode particles in summer and spring.

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 (AE_440-870) 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 AE_440-870 by +0.0009 per year was noted. Seasonal change of AOD₄₄₀ (AE_440-870) 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.

Introduction

Atmospheric aerosol plays a very important role in many atmospheric processes and has a significant direct (due to scattering and absorption of sunlight) and indirect (through interaction with clouds) effect on the radiation balance of the Earth's climate system (Bala et al., 2010; Das et al., 2011; Yu et al., 2016a) as well as cloud formation (Ackerman et al., 2000), hydrologic cycle (Bala et al., 2010), and the photochemistry of the atmosphere (Bai et al., 2018). Aerosols impact air quality (Chubarova et al. 2011, 2016b; Chaikovsky et al., 2014; Kumar et al., 2018; Filonchyk et al., 2020a), visibility range (Singh and Dey 2012; Liao et al., 2015; Huang et al., 2018) and human health (Kinney 2008; Dimitriou et al., 2013; Kim et al., 2015; Liao et al., 2015; Vandyck et al., 2018). With a high degree of spatial-temporal variation, atmospheric aerosols are highly diverse in microphysical, physical and chemical properties (Tiwari et al., 2016; Volkova et al., 2018; Filonchyk et al., 2020b). In the regions where both anthropogenic and natural aerosols play an essential role in climate change, an adequate assessment of man-induced aerosol impact is needed to understand its role in long-term change of climate. This necessitates systematic observation of aerosol optical and microphysical properties with high spatial-temporal resolution.

At present, various satellite and ground-based instruments are widely used to study atmospheric aerosols. Each of these instruments has its strengths and weaknesses. Thus, satellite instruments can give information on aerosol properties both on a global and regional scale for a long period with practically daily temporal scale, however, aerosol types and surface reflectance may affect the quality of aerosol retrievals (Chubarova et al., 2011; Mielonen et al., 2011; Kumar and Devara 2012; Gupta et al., 2016; Priyadharshini et al., 2018). Ground-based remote sensing networks give more precise information about aerosol properties but do not provide continuous global area coverage (Holben et al., 1998; Chaikovsky et al., 2016). The AERONET (AErosol RObotic NETwork) global ground-based network of stations, equipped with sun/sky photometers CIMEL, provides for continuous monitoring of aerosol properties with high temporal resolution. It is an important source of data about variations in columnar aerosol optical properties in different regions. Regular measurements from AERONET enables us to analyze the global and local peculiarities pertinent to the composition of atmospheric aerosols.

The air quality of Eastern Europe, although the largest region of Europe with various sources of aerosol formation, is one of the least studied in the world. Apart from anthropogenic sources, the substantial contribution of aerosol pollution in the region is made by peat and forest fires, geographically situated in Ukraine and Russia (Sitnov et al., 2013; Shvidenko and Schepaschenko 2013; Kabashnikov et al., 2014; Milinevsky et al., 2014 2018; Ulevicius et al., 2016; Filonchyk et al., 2020a). The primary source of air pollution in the larger cities is road transport, accounting for 80% of the total volume of air pollutants (WHO 2002). Some earlier studies reported on the aerosol physical and optical characteristics obtained over different regions of Eastern Europe (Chubarova et al., 2011; Sitnov et al., 2013; Milinevsky et al., 2014; Miatselskaya et al., 2016; Ulevicius et al., 2016; Milinevsky and Danylevsky 2018; Volkova et al., 2018; Filonchyk and Hurynovich 2020; Filonchyk et al., 2020a).

Studies have examined the cities of Moscow, St. Petersburg and Kyiv but only certain optical parameters were studied, such as AOD and AE but with limited data. The physical, chemical and radiative properties of aerosols in the region are still not well documented. The air quality of Minsk, Belarus, where one of the oldest AERONET stations is located, has not been examined. The station started to measure aerosol properties beginning in April 2002 and has been monitoring atmospheric aerosols virtually daily for over 18 years. Studies of optical and radiative properties of aerosol using long-term data are important for regional climatic change assessment. With this regard, it was decided to perform a comprehensive study to investigate the aerosols characteristics in Minsk itself, which is of significant scientific interest.

To assess the ecological state of the atmosphere, study the processes of climate change, enhance the credibility of forecasts and address a great number of other tasks, systematic observations of optical and microphysical aerosol characteristics with high spatial-temporal resolution is needed. This is because atmospheric aerosols are dynamically unsteady and unstable, easily dispersed with prominent spatial-temporal variation. Therefore, this study uses data from the Minsk AERONET station for the period from April 2002 to December 2019. The analysis was carried out for optical, physical and radiative properties of aerosols that include aerosol optical depth (AOD), Ångström exponent (AE), aerosol volume size distribution (VSD), single scattering albedo (SSA), aerosol refractive index (RI), asymmetry parameter (ASY), aerosol radiative forcing (ARF) and aerosol heating rate. Classification of predominant aerosol types in the atmosphere was carried out based on the relationship between AOD and AE.