1Department of Applied Environmental Science (ITM) and Bert Bolin Centre for Climate Research, Stockholm University, S 114 18 Stockholm, Sweden
2Department of Meteorology (MISU) and Bert Bolin Centre for Climate Research, Stockholm University, S 106 91 Stockholm, Sweden
3Division of Nuclear Physics, Lund University, P.O. Box 118, SE-211 00 Lund, Sweden
4Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam, Germany
*now at: Stockholm Environment and Health Administration, P.O. Box 8136, 104 20 Stockholm, Sweden
Received: 25 Nov 2013 – Published in Atmos. Chem. Phys. Discuss.: 17 Mar 2014
Abstract. In this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m−2) in the Arctic at Ny-Ålesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 ± 2.26 (mean ± standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).
Revised: 14 May 2014 – Accepted: 06 Jun 2014 – Published: 21 Jul 2014
Rastak, N., Silvergren, S., Zieger, P., Wideqvist, U., Ström, J., Svenningsson, B., Maturilli, M., Tesche, M., Ekman, A. M. L., Tunved, P., and Riipinen, I.: Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard, Atmos. Chem. Phys., 14, 7445-7460, doi:10.5194/acp-14-7445-2014, 2014.