Climatology of aerosol optical depth over Eastern Europe based on 19 years (2000-2018) MODIS TERRA data

This study investigates the spatial-temporal evolution of aerosols, their optical properties (aerosol optical depth [AOD] and angstrom exponent [AE]) and the trend over a period of 19 years in the Eastern European countries. The data used for the study are from moderate-resolution imaging spectroradiometer (MODIS) Terra Collection 6.1 aerosol products with the use of Dark Target algorithm for the period from 2000 to 2018. The satellite-based AOD products were validated against the AERONET AOD measurements in four stations, located in different regions. The results demonstrate high coherence in the setting of high values of correlation (R = 0.8-0.9) and low values of root-mean-square error (RMSE [0.066-0.130]) and mean absolute error (MAE [0.048-0.067]). However, of the total amount of data from AERONET stations, only 68.9% of available data fall within expected error (EE) over land. Generally, all countries recorded a low AOD (83.2% less than 0.2) and high AE (82.5% higher than 1). Mean AOD and AE values varied from 0.17 +/- 0.12 and 1.31 +/- 0.27 (Russia) to 0.24 +/- 0.14 and 1.31 +/- 0.33 (Czech Republic). There was a gradual decrease in aerosol load in all countries, the highest tendencies of AOD reduction are observed in Czech Republic, Bulgaria, Slovakia and Hungary (by -0.0028, -0.0027, -0.0026 and -0.0025 per year), while the lowest tendencies of reduction are observed in Russia and Moldova (by -0.001 and -0.0006 per year). Seasonal averaged AOD values have maximum values in summer and minimum values in winter. We studied predominant aerosol types, which are based on AOD and AE interrelation, the results showed the predominance of clean continental and mixed aerosols over all countries of the region.