Hygroscopic growth of atmospheric aerosol sampled in Prague 2008 using humidity controlled inlets L. Štefancová a, ⁎, J. Schwarz a , W. Maenhaut b , X. Chi b , J. Smolík a a Institute of Chemical Process Fundamentals of the ASCR. v.v.i., Rozvojová 2, 165 02 Prague 6 - Suchdol, Czech Republic b The Institute for Nuclear Sciences, Ghent University, Proeftuinstraat 86, 9 000 Ghent, Belgium article info abstract Article history: Received 11 March 2010 Accepted 15 April 2010 Atmospheric aerosol was sampled at different humidity conditions using two 7-stage modified BLPI impactors. Dry particles were obtained at 20% RH. Wet particles were humidified inside diffuse humidifier with output 85–90% RH. 11 parallel intakes of dry and wet aerosol were done during winter campaign and 10 during summer one. The samples were processed by gravimetric method, ion chromatography and WSOC analysis. The average mass concentration sampled in winter was 34.4 μg/m 3 at dry, whereas the average mass concentration obtained at wet conditions was slightly higher 37.2 μg/m 3 . The average of summer concentration was 21.4 μg/m 3 at dry conditions, and 21.6 μg/m 3 at wet conditions. Theoretical mass-size distribution of wet aerosol determined from dry aerosol data was calculated using the most abundant hygroscopic inorganic anions SO 4 2- , NO 3 - , Cl - , and WSOC fractions were only taken into account. Calculated distribution estimates the growth of particles due to water uptake and predicts the size distribution of wet aerosol. The growth factors based on Stokes and aerodynamic diameters were calculated. Measured differences in dry and wet size distributions of single species pointed to externally mixed particles and/or changes in aerosol composition during sampling. © 2010 Elsevier B.V. All rights reserved. Keywords: Atmospheric aerosols Mass-size distribution Hygroscopic growth 1. Introduction Ambient aerosol samplings that aimed to particulate matter monitoring, has shown the variations in concentra- tions and chemical compositions of aerosol particles present in the atmosphere spread above Europe. Central European aerosols were found to have a composition which differs from the West European aerosols, due to different industrial activities and air pollution control (Swietlicky and Krejci, 1996). One of the first atmospheric studies in Prague, focused on aerosol size distribution and composition, was done by Hillamo et al., 1999. Lately, several measurements were provided mainly by monitoring PM 10 and PM 2.5 fraction (Sillanpää et al., 2006). Outdoor aerosol samplings included size segregation and chemical resolution measured by Smolík et al., 2008. Elemental and organic carbon determination of urban and suburban aerosols in Prague was recently described in Schwarz et al., 2008. But none of aforementioned experiments dealt with hygroscopic growth of aerosol. One of the first experiments based on hygroscopic growth of aerosol particles was done by Tang et al. (1977, 1978). The studies dealt with activity change of pure inorganic compounds upon different relative humidity. Nowadays the water uptake of aerosol particles is mainly studied by HTDMA technique. This technique has potential to distinguish between particles from different natural and anthropogenic sources by their water uptake ability (Johnson et al., 2004; Aklilu et al., 2006). In all studied cases the hygroscopic behavior of particles depends on their size, chemistry and external mixing (Aklilu and Mozur- kewich, 2004). Therefore the HTDMA resolves the particles with small growth factor (GF) so called “nearly hydrophobic”, with GF smaller then ammonium sulfate “less hydroscopic” and the particles with GF equal and larger than ammonium sulfate that are considered as “more hygroscopic” (Massling et al., 2007; Carrico et al. 2005; Decesari et al., 2000). Depending on Atmospheric Research 98 (2010) 237–248 ⁎ Corresponding author. E-mail address: stefancova@icpf.cas.cz (L. Štefancová). 0169-8095/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2010.04.009 Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos