Hygroscopic growth of atmospheric aerosol sampled in Prague 2008 using humidity controlled inlets

Abstract

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 34.4μg/m3 at dry, whereas the average mass concentration obtained at wet conditions was slightly higher 37.2μg/m3. The average of summer concentration was 21.4μg/m3 at dry conditions, and 21.6μg/m3 at wet conditions. Theoretical mass-size distribution of wet aerosol determined from dry aerosol data was calculated using the most abundant hygroscopic inorganic anions SO42−, NO3−, 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.