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

Abstract

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 10 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 transitions temperatures . We also show that only the diastereomeric isomers differ in their values, albeit only by a few kelvin. We derive the phase diagram of water/tetraol mixtures over the whole tropospheric 15 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-tricaboxylic acid (3-MBTCA). Overall, our results imply a liquid-like state of isoprene-derived SOA 20 particle in the lower troposphere at moderate to high relative humidity, but presumably a semisolid or even glassy state at upper tropospheric conditions, particularly at low relative humidity, thus providing experimental support for recent modelling calculations. 30Atmos. Chem. Phys. Discuss., https://doi

The Cooling Rate- and Volatility-Dependent Glass-Forming Properties of Organic Aerosols Measured by Broadband Dielectric Spectroscopy

“…The glass transition temperatures of ISOPOOH and IEPOX are 142 ± 3 and 166 ± 2 K, respectively, while 2-methyltetrol shows a much higher glass transition temperature of 230 ± 2 K. The glass transition temperature of 2-methyltetrol at a 10 K/min cooling rate is 232 K ± 3 K, which agrees within the error bar range of similar measurements performed by Lessmeier et al using differential scanning calorimetry (DSC). 55 DSC uses faster cooling rates of 10−50 K/min, often leading to a difference of ∼10 K in T g measurement when compared with the BDS method. 56 The 2methyltetrol sulfates with inorganic sulfates mixture have a glass transition temperature of 252 ± 3 K. Each experiment was repeated at least three times to calculate the average relaxation time and the standard deviation at each temperature, as shown in Figure 2 and Figure S3.…”

Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior

“…To account for the influence of water in the atmosphere, we implement the Gordon−Taylor equation (eq 3), 6,13 which incorporates the mass fraction of water (1 − w org , eqs 4 and 5), the glass transition temperature of pure water (T g,w ), the mass fraction of organics (w org , eq 5), the dry glass transition temperature (T g,org ), and the Gordon−Taylor constant (k GT , an interaction parameter used to describe the glass transition temperature of organic−water mixtures, which can vary based on the mixture's constituents 6,7,23 ). We assign each sample a random Gordon−Taylor constant value between 1.05 and 4, 6,7,12,13,23,24…”