title: Comparison of Methods for Predicting the Compositional Dependence of the Density and Refractive Index of Organic-Aqueous Aerosols.
abstract: Representing the physicochemical properties of aerosol particles of complex composition is of crucial importance for understanding and predicting aerosol thermodynamic, kinetic, and optical properties and processes and for interpreting and comparing analysis methods. Here, we consider the representations of the density and refractive index of aqueous-organic aerosol with a particular focus on the dependence of these properties on relative humidity and water content, including an examination of the properties of solution aerosol droplets existing at supersaturated solute concentrations. Using bulk phase measurements of density and refractive index for typical organic aerosol components, we provide robust approaches for the estimation of these properties for aerosol at any intermediate composition between pure water and pure solute. Approximately 70 compounds are considered, including mono-, di- and tricarboxylic acids, alcohols, diols, nitriles, sulfoxides, amides, ethers, sugars, amino acids, aminium sulfates, and polyols. We conclude that the molar refraction mixing rule should be used to predict the refractive index of the solution using a density treatment that assumes ideal mixing or, preferably, a polynomial dependence on the square root of the mass fraction of solute, depending on the solubility limit of the organic component. Although the uncertainties in the density and refractive index predictions depend on the range of subsaturated compositional data available for each compound, typical errors for estimating the solution density and refractive index are less than ±0.1% and ±0.05%, respectively. Owing to the direct connection between molar refraction and the molecular polarizability, along with the availability of group contribution models for predicting molecular polarizability for organic species, our rigorous testing of the molar refraction mixing rule provides a route to predicting refractive indices for aqueous solutions containing organic molecules of arbitrary structure.
authors: The Institute of Chemical Physics, Key Laboratory of Cluster Science, Beijing Institute of Technology , Beijing 100081, People's Republic of China.|School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Chen
authors: C
authors: Cai
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Rachael E H
authors: RE
authors: Miles
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Michael I
authors: MI
authors: Cotterell
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Aleksandra
authors: A
authors: Marsh
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.|Department of Earth and Environmental Sciences, University of Milano-Bicocca , 20124 Milan, Italy.
authors: Grazia
authors: G
authors: Rovelli
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Andrew M J
authors: AM
authors: Rickards
authors: The Institute of Chemical Physics, Key Laboratory of Cluster Science, Beijing Institute of Technology , Beijing 100081, People's Republic of China.
authors: Yun-Hong
authors: YH
authors: Zhang
authors: School of Chemistry, University of Bristol , Bristol, BS8 1TS, U.K.
authors: Jonathan P
authors: JP
authors: Reid