Influence of Functional Groups on the Viscosity of Organic Aerosol

Abstract

Organic aerosols can exist in highly viscous or glassy phase states. A viscosity database for organic compounds with atmospherically relevant functional groups is compiled and analyzed to quantify the influence of number and location of functional groups on viscosity. For weakly functionalized compounds the trend in viscosity sensitivity to functional group addition is carboxylic acid (COOH) ≈ hydroxyl (OH) > nitrate (ONO) > carbonyl (CO) ≈ ester (COO) > methylene (CH). Sensitivities to group addition increase with greater levels of prior functionalization and decreasing temperature. For carboxylic acids a sharp increase in sensitivity is likely present already at the second addition at room temperature. Ring structures increase viscosity relative to linear structures. Sensitivities are correlated with analogously derived sensitivities of vapor pressure reduction. This may be exploited in the future to predict viscosity in numerical models by piggybacking on schemes that track the evolution of organic aerosol volatility with age.

Predicting the glass transition temperature and viscosity of secondary organic material using molecular composition

“…Song et al (2016b) showed that estimations from group contribution approaches combined with either non-ideal or ideal mixing reproduced the RH-dependent trends particularly well for the alcohol, dicarboxylic, and tricarboxylic acid systems with viscosities of up to 10 4 Pa s. In contrast, model calculations overestimated the viscosity of more viscous compounds including monosaccharides, disaccharides, and trisaccharides by many orders of magnitude (Song et al, 2016b). A recent study compiled the viscosity of organic compounds with atmospherically relevant functional groups, investigating the influence of the number and location of functional groups on viscosity (Rothfuss and Petters, 2017a). These studies provide important insights into estimating the viscosity of individual organic compounds.…”

“…Quasi-equilibrium versus kinetically limited or non-equilibrium SOA growth remains an open issue and warrants further investigations. Group contribution methods have been used to predict the viscosities of pure compounds when the functionality and molecular structure are known (Sastri and Rao, 1992;Rothfuss and Petters, 2017a). Song et al (2016b) showed that estimations from group contribution approaches combined with either non-ideal or ideal mixing reproduced the RH-dependent trends particularly well for the alcohol, dicarboxylic, and tricarboxylic acid systems with viscosities of up to 10 4 Pa s. In contrast, model calculations overestimated the viscosity of more viscous compounds including monosaccharides, disaccharides, and trisaccharides by many orders of magnitude (Song et al, 2016b).…”

“…Solid markers represent measured T g of 258 CHO compounds Dette et al, 2014;Rothfuss and Petters, 2017a), while open markers represent 654 CHO compounds in SOA . Markers are color coded by atomic O : C ratio.…”

“…This version of the figure has been updated to include a number of experimentally measured T g values of larger compounds with M up to 1153 g mol −1 , including aliphatic compounds containing OH and/or COOH groups. Specifically, data for 76 aliphatic alcohols, 39 carbohydrates and their derivatives, 4 carboxylic acids, and 4 hydroxy acids, as compiled by Rothfuss and Petters (2017a), have been added to Fig. 1.…”

“…Table 1. Composition classes and the n 0 C and b values (K) for glass transition temperature parameterizations obtained by least-squares optimization using the measurements compiled in Koop et al (2011), Dette et al (2014), and Rothfuss and Petters (2017a). Note that the evaluation dataset used to derive Eq.…”