Aerosol optical properties in Northern Norway and Svalbard.

We present comparisons between estimates of the aerosol optical thickness and the Ångström exponent in Northern Norway and Svalbard based on data from AERONET (Aerosol Robotic Network) stations at Andenes (69.28°N, 16.01°E, 379 m altitude) and Hornsund (77.00°N, 15.56°E, 10 m altitude) for the period 2008-2013. The five/six-year annual mean values for the aerosol optical thickness at 500 nm τ(500) at Andenes and Hornsund both were 0.09. At Hornsund, there was less variation of the monthly mean value of τ(500) than at Andenes. The annual mean values of the Ångström exponent α at Andenes and Hornsund were 1.29 and 1.34, respectively. At Andenes and Hornsund α was found to be larger than 1.1 in 68% and 84% of the observations, respectively, indicating that fine-mode particles were dominating at both sites. Both sites had a similar aerosol size distribution during summer although one site is in an arctic area while the other site is in a subarctic area.