5 1ETH Zurich, Institute for Atmospheric and Climate Science, Switzerland; 6 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; 7 3Institute for Aerosol Sensor Technology, FHNW, Switzerland; 8 4Deutsches Zentrum für Luftund Raumfahrt, Institut für Physik der Atmosphäre, 82234 9 Oberpfaffenhofen, Germany. 10 11 *Now at: Aerosol Consulting ML GmbH, Ennetbaden, Switzerland, & Ecotech Pty Ltd., 12 Australia. **Now at: Institut für Energieund Klimaforschung IEK-8: Troposphäre, 13 Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. 14 15 Combustion-generated particles represent the most absorbing particles in the atmosphere 16 and are estimated to be the strongest anthropogenic climate warming agent after CO2 17 (IPCC, 2007; Ramanathan and Carmichael, 2008; Bond et al., 2013). In addition to direct 18 absorptive heating, such particles may enhance glacial melting, alter convection and 19 precipitation, react with atmospheric trace gases, and serve as cloud condensation or ice 20 nuclei (Bond et al., 2013). Their short atmospheric lifetime of days to weeks (Cape et al., 21 2012) makes them ideal candidates for near-term climate mitigation (Shindell et al., 2012; 22 Bond et al., 2013). However, significant uncertainties in the atmospheric burden and 23 mixing state of different combustion-generated particles lead to large uncertainties in 24 current model predictions (Bond et al., 2013). Such uncertainties may be reduced by the 25 new Aerodyne Soot-Particle Aerosol Mass Spectrometer (SP-AMS), a commercial 26 instrument that can characterize both soot mixing state and chemical composition. 27