Physical properties of ambient and laboratory‐generated secondary organic aerosol

Abstract

The size and thickness of organic aerosol particles collected by impaction in five field campaigns were compared to those of laboratory-generated secondary organic aerosols (SOA). Scanning transmission X-ray microscopy was used to measure the total carbon absorbance (TCA) by individual particles as a function of their projection areas on the substrate. Particles with higher viscosity/surface tension can be identified by a steeper slope on a plot of TCA versus size because they flatten less upon impaction. The slopes of the ambient data are statistically similar indicating a small range of average viscosities/surface tensions across five field campaigns. Steeper slopes were observed for the plots corresponding to ambient particles, while smaller slopes were indicative of the laboratory-generated SOA. This comparison indicates that ambient organic particles have higher viscosities/surface tensions than those typically generated in laboratory SOA studies.

Relative humidity-dependent viscosities of isoprene-derived secondary organic material and atmospheric implications for isoprene-dominant forests

“…8b). This conclusion is consistent with work by O'Brien et al (2014) who also concluded that the viscosity of isoprene-derived particles is lower than the viscosity of α-pinene-derived particles based on the how much the particles flattened after impaction on a substrate. The differences may be due to a difference in the molecular weights of the two SOMs since viscosity can increase as the molecular weight of an organic compound increases (Zobrist et al, 2008;Koop et al, 2011).…”

The Influence of Absolute Mass Loading of Secondary Organic Aerosols on Their Phase State

“…Despite the integral role of SOA in atmospheric processes, there remains a limited understanding of the chemical and physical changes induced in SOA as it is formed and subsequently aged. Understanding the physical state of SOA is especially important, as it can provide insight into SOA formation [12,13] and growth [14], gas-particle partitioning [15], reactive uptake on particle surfaces [16,17], and atmospheric impacts [18][19][20].…”

Airborne soil organic particles generated by precipitation

“…Figure 3c illustrates the heights of the ASOP as a function of particle size (determined as the two-dimensional (2D) projected area equivalent diameter), compared with other organic particles observed at the Southern Great Plains site and previously reported measurements 10 . For a given particle size, ASOP have total carbon absorption values up to ten times larger than particles observed in previous studies 10 . This indicates that ASOP are significantly more viscous (solid) than organic particles reported previously.…”

“…Similarly sized carbonaceous particles with higher total carbon absorption are more viscous or solid (glassy) than those with lower absorption, which is indicative of liquid particles flattened on the substrate 10 . Figure 3c illustrates the heights of the ASOP as a function of particle size (determined as the two-dimensional (2D) projected area equivalent diameter), compared with other organic particles observed at the Southern Great Plains site and previously reported measurements 10 . For a given particle size, ASOP have total carbon absorption values up to ten times larger than particles observed in previous studies 10 .…”