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Volume 18, issue 21 | Copyright
Atmos. Chem. Phys., 18, 15841-15857, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Nov 2018

Research article | 05 Nov 2018

Physical state of 2-methylbutane-1,2,3,4-tetraol in pure and internally mixed aerosols

Jörn Lessmeier1,*, Hans Peter Dette1,*, Adelheid Godt1, and Thomas Koop1 Jörn Lessmeier et al.
  • 1Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
  • *These authors contributed equally to this work.

Abstract. 2-Methylbutane-1,2,3,4-tetraol (hereafter named tetraol) is an important oxidation product of isoprene and can be considered as a marker compound for isoprene-derived secondary organic aerosols (SOAs). Little is known about this compound's physical phase state, although some field observations indicate that isoprene-derived secondary organic aerosols in the tropics tend to be in a liquid rather than a solid state. To gain more knowledge about the possible phase states of tetraol and of tetraol-containing SOA particles, we synthesized tetraol as racemates as well as enantiomerically enriched materials. Subsequently the obtained highly viscous dry liquids were investigated calorimetrically by differential scanning calorimetry revealing subambient glass transition temperatures Tg. We also show that only the diastereomeric isomers differ in their Tg values, albeit only by a few kelvin. We derive the phase diagram of water–tetraol mixtures over the whole tropospheric temperature and humidity range from determining glass transition temperatures and ice melting temperatures of aqueous tetraol mixtures. We also investigated how water diffuses into a sample of dry tetraol. We show that upon water uptake two homogeneous liquid domains form that are separated by a sharp, locally constrained concentration gradient. Finally, we measured the glass transition temperatures of mixtures of tetraol and an important oxidation product of α-pinene-derived SOA: 3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA). Overall, our results imply a liquid-like state of isoprene-derived SOA particles in the lower troposphere at moderate to high relative humidity (RH), but presumably a semisolid or even glassy state at upper tropospheric conditions, particularly at low relative humidity, thus providing experimental support for recent modeling calculations.

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Short summary
We synthesized a compound, a tetraol, which is an atmospheric oxidation product in isoprene-derived secondary organic aerosols, and studied whether the tetraol is liquid or solid depending upon temperature and relative humidity, both in pure form and in mixtures with other compounds. Our results imply a liquid state of isoprene-derived aerosol particles in the lower troposphere at moderate humidity, but a solid state at colder upper tropospheric conditions, thus supporting modeling calculations.
We synthesized a compound, a tetraol, which is an atmospheric oxidation product in...