Research Output per year
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.
|Date made available||21 Sep 2016|
|Publisher||University of Bristol|
Haddrell, A., Bzdek, B., Reid, J., Bannan, T., Topping, D., Percival, C. J. & Cai, C., 20 Oct 2016, In : Journal of Physical Chemistry A. 120, 41, p. 8123–8137 5 p.
Research output: Contribution to journal › Article (Academic Journal)
46 Citations (Scopus)
312 Downloads (Pure)
Projects per year
1/12/14 → 31/03/18
Bzdek, B. (Creator), Haddrell, A. (Creator), Reid, J. (Creator), Miles, R. (Creator) (21 Sep 2016). Measurements and Predictions of Binary Component Aerosol Particle Viscosity (J Phys Chem A, 2016). University of Bristol. 10.5523/bris.gelaxwmkbqz91h9t54467wpsw