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 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.

Predictions of the glass transition temperature and viscosity of organic aerosols from volatility distributions

“…The SOA simulations applying the VBS framework have not yet included the effects of viscosity on SOA formation and evolution. When the gasparticle partitioning is limited by bulk diffusion, kinetic treatments of SOA partitioning may need to be applied (Perraud et al, 2012;Liu et al, 2016;Yli-Juuti et al, 2017;Li and Shiraiwa, 2019). Some chamber experiments probing the mixing timescales of SOA particles formed from isoprene, α-pinene, and limonene did not observe significant kinetic limitations at moderate and high RH under room temperature conditions (Loza et al, 2013;Ye et al, 2016), while kinetic limitations of bulk diffusion of organic molecules in β-caryophyllene SOA have been observed at 75 % RH (Ye et al, 2018), warranting further investigations on the degree of kinetic limitations in ambient tropospheric conditions.…”

Hygroscopic behavior of aerosols generated from solutions of 3-methyl-1,2,3-butanetricarboxylic acid, its sodium salts, and its mixtures with NaCl

“…MBTCA was first observed in the Amazon Basin and in summer aerosols from Ghent, Belgium (Kubátová et al, 2000;Kubátová et al, 2002). The compound was later found in the USA (Jaoui et al, 2005), Europe (Fu et al, 2009;Kourtchev et al, 2009;Zhang et al, 2010;Yasmeen et al, 2011;Gómez-González et al, 2012;Vogel et al, 2013;Kammer et al, 2018;Vlachou et al, 2019), Japan (Miyazaki et al, 2012), the polar regions (Hu et al, 2013), China (Hu et al, 2008;Ding et al, 2012;Li et al, 2013;Fu et al, 2014;Kang et al, 2018;Hong et al, 2019), and Australia (Cui et al, 2019). In addition, it has been observed in forest, marine, mountainous, urban, and rural aerosols, with its levels ranging from 0.03 to 100 ng m −3 , and the level was generally higher in the fine-particle fraction than in the coarse fraction (Zhang et al, 2010).…”

Hygroscopic behavior of aerosols generated from solutions of 3-methyl-1,2,3-butanetricarboxylic acid, its sodium salts, and its mixtures with NaCl

“…Previous studies reported that α-pinene SOAs were very likely to exist as a highly viscous semisolid or even glassy state at low humidity (Saukko et al, 2012;Renbaum-Wolff et al, 2013;Berkemeier et al, 2014;Dette et al, 2014;Kidd et al, 2014;Song et al, 2016;Lessmeier et al, 2018). In addition, many organic substances, such as carboxylic acids, carbohydrates, and proteins, tend to form amorphous rather than crystalline phases upon the drying of aqueous solution droplets (Mikhailov et al, 2009).…”