Contribution of carbonaceous material to cloud condensation nuclei concentrations in European background (Mt. Sonnblick) and urban (Vienna) aerosols

During four intensive measurement campaigns (two on Mt. Sonnblick, European background aerosol, and two in Vienna, urban aerosol), cloud condensation nuclei (CCN) were measured at supersaturations of 0.5%. Impactor measurements of the mass size distribution in the size range 0.1-10 mu m were performed and later analyzed for Cl-, NO3-, SO42-, Na+, NH4+ , K+, Ca2+ and Mg2+ by ion chromatography, for total carbon (TC) using a combustion method, and for black carbon (BC) by an optical method (integrating sphere). Organic carbon (OC) was defined as the difference between TC (minus carbonate carbon) and BC. At all sites, the mass fraction of BC in the submicron aerosol was comparable (4-5%). CCN concentrations on MI. Sonnblick were found to be 10-30% of those measured in Vienna, although high Mt. Sonnblick concentrations were comparable to low Vienna concentrations (around 800 cm(-3)). The contribution of organic material was estimated from the mass concentrations of the chemical species sampled on the impactor stage with the lowest cut point (0.1-0.215 mu m aerodynamic equivalent diameter). On Mt. Sonnblick, TC material contributed 11% to the total mass in fall 1995, and 67% in summer 1996, while the OC fraction was 6 and 61%. The combined electrolytes and mineral material contributed 18 and 16% in fall and summer. During the Vienna spring campaign, the contributions of OC and electrolytes to the total mass concentration in this size range were 48 and 36%, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.