Measurement of internal and external mixtures of test aerosols with a new Single Particle Aerosol Mass Spectrometer

The mixing state of atmospheric aerosol particles is a very important property affecting processes such as CCN
activation and scattering and absorption of light by the particles, but is challenging to determine. A new Single
Particle Aerosol Mass Spectrometer (LAAPTOF, AeroMegt GmbH) was tested with regards to its capability of
measuring internal and external mixture of aerosols using laboratory generated particles. To create the external
mixture, solutions of three different salts in deionized water, and a suspension of carbon black (Cabot Corporation)
in a mixture of isopropanol and water were nebulized and individually dried, before being passed into a small
mixing chamber. To create the internal mixture, equal parts of each solution/suspension were mixed, fed into
a single nebulizer, nebulized and dried. The LAAPTOF sampled from the mixing chamber and recorded mass
spectra of individual particles. The analysis shows a heterogeneous ensemble of single particle spectra for the
external mixture, and a homogeneous ensemble of spectra for the internal mixture. The ability of a fuzzy clustering
algorithm to resolve the difference between the two mixing states was also tested.