A B S T R A C T The aim of this study is to explain the relationship between changes in the amount of low-level cloudiness, the frequency of occurrence of certain types of clouds, the aerosol optical thickness (AOT) of the atmosphere, and changes in relative sunshine duration in Poland in the years 1980-2018. The analytical part of the study first presents the spatial variability of area-average values of the discussed characteristics in seasonal terms, and then shows the strength and direction

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... of trends of individual elements for each of the analysed meteorological stations and averaged over the entire country. In the next stage of the work, the impact of individual cloud types and the aerosol optical thickness of the atmosphere on the multi-annual changes in sunshine duration in Poland was assessed. As a result of the conducted research, a growing trend in area-average values of relative sunshine duration in each season of the year was found in Poland, the highest being in the spring and the smallest in the winter. It was shown that a reduction in aerosol optical thickness and a decrease in the incidence of low-level clouds, including mainly stratiform clouds, had the greatest impact on the changes in sunshine duration.