Journal article

Deliquescence, efflorescence, and phase miscibility of mixed particles of ammonium sulfate and isoprene-derived secondary organic material

Smith M, Bertram A, Martin S ...see all

Atmospheric Chemistry and Physics, vol. 12, issue 20 (2012) pp. 9613-9628

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The hygroscopic phase transitions of ammonium sulfate mixed with isoprene-derived secondary organic material were investigated in aerosol experiments. The organic material was produced by isoprene photo-oxidation at 40% and 60% relative humidity. The low volatility fraction of the photo-oxidation products condensed onto ammonium sulfate particles. The particle-phase organic material had oxygen-to-carbon ratios of 0.67 to 0.74 (+/- 0.2) for mass concentrations of 20 to 30 mu g m(-3). The deliquescence, efflorescence, and phase miscibility of the mixed particles were investigated using a dual arm tandem differential mobility analyzer. The isoprene photo-oxidation products induced deviations in behavior relative to pure ammonium sulfate. Compared to an efflorescence relative humidity (ERH) of 30 to 35% for pure ammonium sulfate, efflorescence was eliminated for aqueous particles having organic volume fractions epsilon of 0.6 and greater. Compared to a deliquescence relative humidity (DRH) of 80% for pure ammonium sulfate, the DRH steadily decreased with increasing epsilon, approaching a DRH of 40% for epsilon of 0.9. Parameterizations of the DRH(epsilon) and ERH(epsilon) curves were as follows: DRH(epsilon) = Sigma(i)c(i),d(epsilon i) valid for 0

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  • M. L. Smith

  • A. K. Bertram

  • S. T. Martin

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