National Research Council of Canada. Measurement Science and Standards
Mixing state refers to the relative proportions of chemical species in an aerosol, and the way these species
are combined; either as a population where each particle consists of a single species (‘externallymixed’) or
where all particles individually consist of two or more species (‘internally mixed’) or the casewhere some
particles are pure and some particles consist of multiple species. The mixing state affects optical and
hygroscopic properties, and quantifying it is therefore important for studying an aerosol’s climate impact.
In this article, we describe a method to quantify the volatile mixing state of an aerosol using a differential
mobility analyzer, centrifugal particle mass analyzer, catalytic denuder, and condensation particle counter
by measuring the mass distributions of the volatile and non-volatile components of an aerosol and
determining how the material is mixed within and between particles as a function of mobility diameter.
Themethod is demonstrated using two aerosol samples from aminiCAST soot generator, one with a high
elemental carbon (EC) content, and one with a high organic carbon (OC) content. The measurements are
presented in terms of themass distribution of the volatile and non-volatilematerial, as well asmeasures of
diversity and mixing state parameter. It was found that the high-EC soot nearly consisted of only pure
particles where 86% of the total mass was non-volatile. The high-OC soot consisted of either pure volatile
particles or particles that contained a mixture of volatile and non-volatile material where 8% of the total
mass was pure volatile particles and 70% was non-volatile material (with the remaining 22% being volatile
material condensed on non-volatile particles).