Colloquium: Tuesday, September 18, 2007, EN6085A, 3:00 pm.

Laboratory measurements of the physical and chemical properties of submicrometric combustion-generated aerosols are presented.  This work probes three questions: 1) What can be learned by performing multi-instrument studies of aerosols synthesized to mimic biomass combustion aerosols?  2) How good of agreement is there between cloud condensation nuclei (CCN) measurements reported by different measurement techniques? 3) Can combustion-generated aerosols act as CCN in atmospheric clouds? 

Synthesized combustion aerosols were prepared at the Leipzig Aerosol Cloud Interaction Simulator (LACIS) facility.  Monodisperse particles composed of soot, soot coated with ammonium sulfate, soot coated with levoglucosan and soot coated with both ammonium sulfate and levoglucosan were produced and tested.   Levoglucosan is a low molecular weight organic, a tracer of cellulose combustion and is moderately hygroscopic.

Included in the study were two Wyoming static diffusion CCN instruments, the continuous-flow instrument built by Droplet Measurement Technology, the continuous-flow LACIS instrument, operated in CCN mode, a hygroscopic tandem differential mobility analyzer and two aerosol mass spectrometers.   The comparison of critical CCN supersaturations, derived from measurements made by four CCN instruments, is quite encouraging.   With few exceptions the critical supersaturations agree within the known uncertainties.

In addition, this work reveals a contradiction between CCN measurement and a Köhler model prediction of the critical supersaturation of pure levoglucosan particles.   Also unreconciled are CCN measurements and mass spectrum-based estimates of the critical supersaturation of levoglucosan-coated soot particles.