Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 6 2005 10.5194/acpd-5-11703-2005 http://www.atmos-chem-phys-discuss.net/5/11703/2005/ http://www.atmos-chem-phys-discuss.net/5/11703/2005/acpd-5-11703-2005.html http://www.atmos-chem-phys-discuss.net/5/11703/2005/acpd-5-11703-2005.pdf 11703 11728 2005-11-15 Measurements of optical properties of atmospheric aerosols in Northern Finland V. Aaltonen veijo.aaltonen@fmi.fi H. Lihavainen V.-M. Kerminen M. Komppula J. Hatakka K. Eneroth M. Kulmala Y. Viisanen Climate and Global Change Research, Finnish Meteorological Institute, P.O. Box 503, 00 101 Helsinki, Finland Department of Applied Environmental Science, Stockholm University, 10 691 Stockholm, Sweden Department of Physical Sciences, Division of Atmospheric Sciences, P.O. Box 64, 00 014 University of Helsinki, Finland Three years of continuous measurements of aerosol optical properties and simultaneous aerosol number size distribution measurements at Pallas GAW station, a remote subarctic site in the northern border of the boreal forest zone, have been analysed. The scattering coefficient at 550 nm varied from 0.2 to 94.4 Mm^−1 with an average of 7.1±8.6 Mm^−1. Both the scattering and backscattering coefficients had a clear seasonal cycle with an autumn minimum and a 4–5 times higher summer maximum. The scattering was dominated by submicron aerosols and especially so during late summer and autumn. The Ångström exponent had a clear seasonal pattern with maximum values in late summer and minimum values during wintertime. The highest hemispheric backscattering fraction values were observed in autumn, indicating clean air with few scattering particles and a particle size distribution strongly dominated by ultrafine particles. To analyse the influence of air mass origin on the aerosol optical properties a trajectory climatology was applied to the Pallas aerosol data. The most polluted trajectory patterns represented air masses from the Kola Peninsula, Scandinavia and Russia as well as long-range transport from Britain and Eastern Europe. These air masses had the largest average scattering and backscattering coefficients for all seasons. Higher than average values of the Ångström exponent were also observed in connection with transport from these areas.