Most aerosol particles in the atmosphere contain both inorganic and organic components.  While the interactions of water vapor with most inorganic components are well-characterized, the presence of a complex organic phase can modify water uptake. To explore these effects, hygroscopicity tandem differential mobility analysis experiments were performed.   Water uptake was quantified on mixed aerosol containing ammonium sulfate (AS) and semi-solid reaction products of aldehyde-amine reactions, on aldehyde-AS reaction products, and on fresh mixtures of aldehydes and AS.  All mixed aerosol particles deliquesced at relative humidity (DRH) levels slightly below that of pure AS: the presence of organics caused up to a 12% reduction in DRH and up to a 10% reduction in the hygroscopic growth factor at 80% RH. Glyoxal-AS aerosol, on the other hand, did not undergo prompt deliquescence, even though these particles contained excess unreacted AS. Instead, both reacted and freshly-mixed glyoxal-AS aerosol took up water continuously beyond 45% RH.  Particle imaging shows that glyoxal-AS aerosol particles become amorphous semi-solids when dried, which suggests that oligomerized glyoxal-AS reaction products prevent AS from efflorescing during drying.  For the other systems studied, the RH level at which the organic phase becomes semi-solid must be below that where liquid-liquid phase separation occurs. This was confirmed for aldehyde-methylamine-AS aerosol using Raman microscopy measurements of the semi-solid transition as a function of RH and temperature.

Prompt and slow deliquescence of semi-solid, oligomerized aqueous secondary organic aerosol mixed with ammonium sulfate

248th National Meeting (2014)

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