ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-1885-2004 Soot aging time scales in polluted regions during day and night Riemer N. 1 Vogel H. 2 Vogel B. 2 Center for Turbulence Research, Stanford University, Stanford, USA Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe, Karlsruhe, Germany 15 09 2004 4 7 1885 1893 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/1885/2004/acp-4-1885-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/1885/2004/acp-4-1885-2004.pdf

The aging of soot is one of the key uncertainties in the estimation of both the direct and indirect climate effect. While freshly emitted soot is initially hydrophobic and externally mixed, it can be transferred into an internal mixture by coagulation, condensation or photochemical processes. These aging processes affect the hygroscopic qualities and hence the growth behaviour, the optical properties and eventually the lifetime of the soot particles. However, due to computational limits the aging of soot in global climate models is often only parameterised by an estimated turnover rate resulting in a lifetime of soot of several days. Hence, the aging process of soot is one of the key uncertainties governing the burden and effect of black carbon. In this study, we discuss the time scale on which diesel soot is transferred from an external to an internal mixture based on the results of our simulations with a comprehensive mesoscale model. For daytime conditions during summer condensation of sulphuric acid is dominant and the aging process occurs on a time scale of τ =8h close to the sources and τ =2h above the source region. During winter comparable time scales are found but ammonium nitrate becomes more important. During night time condensation is not effective. Then coagulation is the most important aging process and our results show time scales between 10h and 40h.