Soluble mass, hygroscopic growth, and droplet activation of coated soot particles during LACIS Experiment in November (LExNo)

The LACIS Experiment in November (LExNo) campaign was conducted in November 2005 at the Atmospheric Composition Change the European Network of Excellence (ACCENT) site Leipzig Aerosol Cloud Interaction Simulator (LACIS). The goal of LExNo was to provide deeper insight into the activation properties of coated soot particles imitating aged combustion aerosol particles. The aerosols were prepared by starting with spark-generated soot particles. In some experiments the soot particles were compacted by exposure to propanol vapor; in others this step was bypassed. The soot was thermally coated with ammonium sulfate, levoglucosan, or a mixture of both ammonium sulfate and levoglucosan. The synthesized particles were investigated using aerosol mass spectrometry, a Hygroscopicity Tandem differential mobility analyzer, two Wyoming static diffusion cloud condensation nuclei (CCN) instruments, a Droplet Measurement Technologies continuous flow CCN instrument, and LACIS. A close correlation between the hygroscopic growth factor at 98% relative humidity and the critical supersaturation of CCN activation was observed. Closure between hygroscopic growth, CCN activation, and chemical composition of the investigated particles was achieved with two different single-parameter Kohler model approaches and with a third approach, a standard Kohler model using as input parameter the soluble mass as determined by aerosol mass spectrometry.