Voltages are measured by a sun photometer, type SP1a by Dr. Schulz & Partner GmbH in 17 wavelengths between λ = 369nm to 1023nm with a field of view of 1° × 1° and a time resolution of 1 minute. In winter 2012/13 a new sun photometer was installed and just 10 of 17 wavelengths remained in the same wavelength range. With the nine out of ten wavelengths optical parameters like the AOD are computed. The one, which is devoted to water vapor is omitted. The instrument is calibrated regularly in pristine conditions at Izaña, Tenerife, via Langley method.The number of individual measurements differs between a few hundreds, especially in March and September, to up to 12,000 in early summer. No trend in each month can be seen comparing the amount of cloud-free measurements over the years. Only an annual cycle due to polar day and night is included in the data. Due to the instrument data is only available in clear sky conditions.

This data set is only the raw data corresponding to doi:10.1594/PANGAEA.937545 . No calculation, for example for AOD, is done, but can be performed by everyone with the provided data in the following way (the gauge values of every day can be found in the header):1) spectra transmission: TR = (U20/UE KFM)^(1/M), with U20: measured voltage, UE: gauge voltage/extraterrestrial signal, KFM = solar eccentricity, M: air mass2) total AOD: tau_G = |ln(TR)|3) ozone AOD: tau_O3 = (O3_Dob * O3_Gaug) / 1000, with O3_Dob: external measurement value for total ozone concentration in column [DU], O3_Gaug: Gauge value of filter4) AOD of Rayleigh atmosphere: tau_R = P/P0 * (0.00865λ^ex), ex = - (3.9164 + 0.074*λ + 0.05/λ), with P = 1013.25hPa, P0: pressure at measurement point [hPa], λ: wavelength of filter [µm]5) AOD of aerosol: tau_AE = tau_G - tau_R - tau_O3 ---The data is a tar.gz file. Each measurement day contains in netcdf format the following variables:Time (minutes after midnight UTC)wavelengths ([nm], lambda)pressure [hPa]voltage [V]Header with gauge values