Methodology for quantifying the volatile mixing state of an aerosol

Abstract

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 ('externally mixed') or where all particles individually consist of two or more species ('internally mixed') or the case where 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. The method is demonstrated using two aerosol samples from a miniCAST 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 the mass distribution of the volatile and non-volatile material, as well as measures 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).

Effective density and volatility of particles sampled from a helicopter gas turbine engine

“…Note that this measurement is independent of the particle losses in the hot or cold stripper, as particle losses in the strippers do not affect the median mass of the distribution measured by CPMA because the particles going through the strippers have the same mobility (Dickau et al, 2016).…”

“…All instruments used in this study are identical to those in Dickau et al (2016). Figure 1 shows the experimental setup used to measure the Gnome particle emissions.…”

“…The effective density and the size-segregated volatility measurements followed the methodology of Dickau et al (2016), which is described briefly here. All instruments used in this study are identical to those in Dickau et al (2016).…”

Machine Learning to Predict the Global Distribution of Aerosol Mixing State Metrics

“…It can refer to individual chemical species, as in the studies by Riemer and West [13], Healy et al [15], O'Brien et al [16], Giorio et al [24], and Fraund et al [25]. Alternatively, it can refer to species groups, as in Dickau et al [26] who quantified mixing state with respect to volatile and non-volatile components. Since we are concerned with CCN properties in this paper, we will group the chemical model species according to hygroscopicity, defining two species groups.…”

Diverse Chemical Mixing States of Aerosol Particles in the Southeastern United States

“…This methodology has been applied to a handful of laboratory and field studies, to date. In the laboratory, Dickau et al (2016) used aerosol sizing and mass instrumentation to quantify the volatile mixing state of soot. Single particle mass spectrometry data from field studies in London 25 (Giorio et al, 2015) and as part the MEGAPOLI campaign in Paris (Healy et al, 2014b) found mixing state was dependent both upon time of day and air mass origin.…”