Measurements and Predictions of Binary Component Aerosol Particle Viscosity (J Phys Chem A, 2016)

Organic aerosol particles are known to often absorb/desorb water continuously with change in gas phase relative humidity (RH) without crystallisation. Indeed, the prevalence of metastable ultraviscous liquid or amorphous phases in aerosol is well-established with solutes often far exceeding bulk phase solubility limits. Particles are expected to become increasingly viscous with drying, a consequence of the plasticising effect of water. We report here measurements of the variation in aerosol particle viscosity with RH (equal to condensed phase water activity) for a range of organic solutes including alcohols (diols to hexols), saccharides (mono-, di- and tri-) and carboxylic acids (di-, tri- and mixtures). Particle viscosities are measured over a wide range (10^-3 to 10^10 Pa s) using aerosol optical tweezers, inferring the viscosity from the timescale for a composite particle to relax to a perfect sphere following the coalescence of two particles. Aerosol measurements compare well with bulk phase studies (well-within an order of magnitude deviation at worst) over ranges of water activity accessible to both. Predictions of pure component viscosity from group contribution approaches combined with either non-ideal or ideal mixing reproduce the RH-dependent trends particularly well for the alcohol, di- and tri-carboxylic acid systems extending up to viscosities of 10^4 Pa s. By contrast, predictions over-estimate the viscosity by many orders of magnitude for the mono-, di-, and tri-saccharide systems, components for which the pure component sub-cooled melt viscosities are >>10^12 Pa s. When combined with a typical scheme for simulating the oxidation of a-pinene, a typical atmospheric pathway to secondary organic aerosol (SOA), these predictive tools suggest that the pure component viscosities are less than 10^6 Pa s for ~97% of the 50,000 chemical products included in the scheme. These component viscosities are consistent with the conclusion that the viscosity of a-pinene SOA is most likely in the range 10^5 to 10^8 Pa s. Potential improvements to the group contribution predictive tools for pure component viscosities are considered.

Creator(s) Bryan Bzdek, Jonathan Reid, Allen Haddrell, Rachael Miles
Funder Engineering and Physical Sciences Research Council, NERC
Publication date 21 Sep 2016
Language eng
Publisher University of Bristol
Licence Non-Commercial Government Licence for public sector information
DOI 10.5523/bris.gelaxwmkbqz91h9t54467wpsw
Complete download (zip) http://data.bris.ac.uk/datasets/gelaxwmkbqz91h9t54467wpsw/gelaxwmkbqz91h9t54467wpsw.zip
Citation Bryan Bzdek, Jonathan Reid, Allen Haddrell, Rachael Miles (2016): Measurements and Predictions of Binary Component Aerosol Particle Viscosity (J Phys Chem A, 2016). https://doi.org/10.5523/bris.gelaxwmkbqz91h9t54467wpsw
Total size 1.2 MiB

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