Tuesday, 6 September 2005 - 8:50 AM

This presentation is part of: Compound Specific Analysis and Preparation

Contributions of fossil fuel, biomass burning, and biogenic emissions to carbonaceous aerosols in Zürich as traced by 14C

Soenke Szidat1, Theo M. Jenk1, Hans-Arno Synal2, Markus Kalberer3, Lukas Wacker4, Irka Hajdas5, Anne Kasper-Giebl6, and Urs Baltensperger7. (1) Laboratory of Environmental Chemistry and Radiochemistry, University of Berne, Freiestrasse 3, Bern, Switzerland, (2) Paul Scherrer Institut (PSI), c/o Institute for Particle Physics, ETH Hönggerberg, Zürich, Switzerland, (3) Laboratory of Organic Chemistry, ETH Zürich, ETH Hönggerberg, Zürich, Switzerland, (4) Institute for Particle Physics, ETH Zürich, ETH Hönggerberg, Zürich, Switzerland, (5) AMS 14C Lab, ETH /PSI, ETH Hönggerberg, Zürich, Switzerland, (6) Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria, (7) Laboratory of Atmospheric Chemistry, Paul Scherrer Institut (PSI), Villigen-PSI, Switzerland

Fine aerosols are important for the earth's climate, by scattering and absorbing sunlight (direct effect) and by modifying cloud characteristics (indirect effect). Furthermore, they have a negative impact on human health, as they contribute to respiratory and cardiopulmonary diseases and mortality. Although carbonaceous particles are a major component of the fine aerosol, there is a large uncertainty about the importance of biogenic and anthropogenic emission sources of these particles. For the identification and quantification of these sources, many elemental and organic molecular tracers have been employed, but their reliability often suffers from limited atmospheric lifetimes due to their chemical reactivity and highly variable emission factors. In contrast to these tracers, 14C determinations offer a unique possibility for unambiguous source apportionment of carbonaceous aerosol particles due to a direct distinction of contemporary and fossil carbon.

In this work, 14C/12C measurements of individual fractions of the carbonaceous aerosol were performed for source apportionment using a recently developed microanalytical technique. This new method goes far beyond the analysis of 14C in total carbon (TC) alone, as often performed previously. We analyzed 14C in elemental carbon (EC) and different organic carbon (OC) fractions from ambient urban aerosols collected in Zürich (Switzerland). This allowed a source attribution of the entire carbonaceous aerosol mass, which is not possible with other currently available methods. The three major sources – fossil fuel, wood combustion (both anthropogenic emissions), and biogenic emissions – were identified making specific regulatory air quality management measures possible. For OC, biogenic sources are dominant in summer with 60 %. Wood combustion accounts for up to 41 % in winter, even though this source contributes only marginally to the local energy consumption. Fossil fuels represent ~30% of OC throughout the year.

This work is supported by the Swiss National Science Foundation (projects 2169-061393.00 and 200020-103605.00).


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