Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard

Abstract

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, 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 and September), when small particles (< 100 nm in diameter) dominate the aerosol size distribution. The maximum scattering by dry particles was observed during Arctic haze period (March, April and May) when 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 on the surface, with the smallest effect during the haze period (March, April and May) and the highest during late summer and beginning of fall (July, August and September).