1School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
2Department of Earth and Environmental Sciences, University of
Milano-Bicocca, 20124 Milan, Italy
3School of Environmental Sciences, University of East Anglia,
Norwich NR4 7TJ, UK
Received: 27 Oct 2016 – Discussion started: 01 Nov 2016
Abstract. Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically < ±0.2 % at water activities > 0.9 and ∼ ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range.
Revised: 10 Feb 2017 – Accepted: 09 Mar 2017 – Published: 31 Mar 2017
Rovelli, G., Miles, R. E. H., Reid, J. P., and Clegg, S. L.: Hygroscopic properties of aminium sulfate aerosols, Atmos. Chem. Phys., 17, 4369-4385, doi:10.5194/acp-17-4369-2017, 2017.