The Long-Term (1964-2014) Variability of Aerosol Optical Thickness and its Impact on Solar Irradiance Based on the Data Taken at Belsk, Poland

Measurements of the Linke turbidity factor (LTF) were performed at Belsk (20.78 degrees E, 51.83 degrees N), Poland, since 1964. This data is used to retrieve broadband aerosol optical thickness normalized to the air mass equal to 2 (BAOT2). A linear analysis of the BAOT2 changes reveals an upward trend of 0.023 +/- 0.017(2 sigma) in the 1964-1975 period, a downward trend of -0.051 +/- 0.017(2 sigma) in the 1976-1991 period, and afterwards a statistically insignificant trend of -0.009 +/- 0.014(2 sigma). Such pattern may be related to the economic changes in Poland (changing emissions and environmental policies). The elevated BAOT2 values, excluded from the trend, are found in 1984 and 1992 due to the volcanic eruptions of El Chichon and Mt. Pinatubo, respectively. Past AOT values at 340 and 500 nm are reconstructed using a linear relationship found between AOT and BAOT2. The reconstructed data is used by the radiative transfer models to estimate a response of the total solar and erythemal radiation to the changes in the atmospheric aerosols at Belsk.