Abstract
Abstract. Volatility and viscosity are important properties of organic aerosols (OA), affecting aerosol processes such as formation, evolution, and partitioning of OA. Volatility distributions of ambient OA particles have often been measured, while viscosity measurements are scarce. We have previously developed a method to estimate the glass transition temperature (Tg) of an organic compound containing carbon, hydrogen, and oxygen. Based on analysis of over 2400 organic compounds including oxygenated organic compounds, as well as nitrogen- and sulfur-containing organic compounds, we extend this method to include nitrogen- and sulfur-containing compounds based on elemental composition. In addition, parameterizations are developed to predict Tg as a function of volatility and the atomic oxygen-to-carbon ratio based on a negative correlation between Tg and volatility. This prediction method of Tg is applied to ambient observations of volatility distributions at 11 field sites. The predicted Tg values of OA under dry conditions vary mainly from 290 to 339 K and the predicted viscosities are consistent with the results of ambient particle-phase-state measurements in the southeastern US and the Amazonian rain forest. Reducing the uncertainties in measured volatility distributions would improve predictions of viscosity, especially at low relative humidity. We also predict the Tg of OA components identified via positive matrix factorization of aerosol mass spectrometer (AMS) data. The predicted viscosity of oxidized OA is consistent with previously reported viscosity of secondary organic aerosols (SOA) derived from α-pinene, toluene, isoprene epoxydiol (IEPOX), and diesel fuel. Comparison of the predicted viscosity based on the observed volatility distributions with the viscosity simulated by a chemical transport model implies that missing low volatility compounds in a global model can lead to underestimation of OA viscosity at some sites. The relation between volatility and viscosity can be applied in the molecular corridor or volatility basis set approaches to improve OA simulations in chemical transport models by consideration of effects of particle viscosity in OA formation and evolution.
Highlights
Organic aerosols (OA) contribute substantially to the mass loadings of atmospheric fine particulate matter (Hallquist et al, 2009; Jimenez et al, 2009)
The marker edge color represents OA components identified via positive matrix factorization of aerosol mass spectrometer (AMS) mass spectra (Lanz et al, 2007), including biomass-burning OA (BBOA), hydrocarbon-like OA (HOA), cooking OA (COA), and oxygenated OA (OOA), which is sometimes further separated into more oxygenated OA (MOOOA) and less oxygenated OA (LO-OOA) factors
We have developed parameterizations to estimate the glass transition temperature of organic compounds using saturation mass concentration (C0) and atomic O : C ratio
Summary
Organic aerosols (OA) contribute substantially to the mass loadings of atmospheric fine particulate matter (Hallquist et al, 2009; Jimenez et al, 2009). We have recently developed a set of semiempirical parameterizations using molar mass (M) and atomic O : C ratio (Shiraiwa et al, 2017) or elemental composition (DeRieux et al, 2018) to predict Tg for compounds comprised of carbon, hydrogen, and oxygen (CHO compounds) These parameterizations have been applied to high-resolution mass spectrometry measurements to estimate viscosity of organic aerosols (DeRieux et al, 2018; Schum et al, 2018; Ditto et al, 2019; Song et al, 2019) and coupled into a thermodynamic model (Gervasi et al, 2020).
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