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Accurate Measurements of Aerosol Hygroscopic Growth Over a Wide Range in Relative Humidity

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Original languageEnglish
Pages (from-to)4376-4388
Number of pages13
JournalJournal of Physical Chemistry A
Volume120
Issue number25
Early online date10 Jun 2016
DOIs
DateAccepted/In press - 10 Jun 2016
DateE-pub ahead of print - 10 Jun 2016
DatePublished (current) - 30 Jun 2016

Abstract

Using a comparative evaporation kinetics approach, we describe a new and accurate method for determining the equilibrium hygroscopic growth of aerosol droplets. The time-evolving size of an aqueous droplet, as it evaporates to a steady size and composition that is in equilibrium with the gas phase relative humidity, is used to determine the time-dependent mass flux of water, yielding information on the vapour pressure of water above the droplet surface at every instant in time. Accurate characterization of the gas phase relative humidity is provided from a control measurement of the evaporation profile of a droplet of know equilibrium properties, either a pure water droplet or a sodium chloride droplet. In combination, and by comparison with simulations that account for both the heat and mass transport governing the droplet evaporation kinetics, these measurements allow accurate retrieval of the equilibrium properties of the solution droplet (i.e. the variations with water activity in the mass fraction of solute, diameter growth factor, osmotic coefficient or number of water molecules per solute molecule). Hygroscopicity measurements can be made over a wide range in water activity (from >0.99 to, in principle, <0.05) on timescales of <10 s for droplets containing involatile or volatile solutes. The approach is benchmarked for binary and ternary inorganic solution aerosols with typical uncertainties in water activity of <±0.2 % at water activities >0.9 and ~±1 % below 80 % RH, and maximum uncertainties in diameter growth factor of ±0.7 %. For all of the inorganic systems examined, the timedependent data are consistent with large values of the mass accommodation (or evaporation) coefficient (>0.1).

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  • EDB_technique_paper_rev

    Rights statement: This is the author accepted manuscript (AAM). The final published version (version of record) is available online via ACS at http://pubs.acs.org/doi/abs/10.1021/acs.jpca.6b04194. Please refer to any applicable terms of use of the publisher.

    Accepted author manuscript, 1 MB, PDF document

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