Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published August 24, 2010 | Published
Journal Article Open

Computation of liquid-liquid equilibria and phase stabilities: implications for RH-dependent gas/particle partitioning of organic-inorganic aerosols


Semivolatile organic and inorganic aerosol species partition between the gas and aerosol particle phases to maintain thermodynamic equilibrium. Liquid-liquid phase separation into an organic-rich and an aqueous electrolyte phase can occur in the aerosol as a result of the salting-out effect. Such liquid-liquid equilibria (LLE) affect the gas/particle partitioning of the different semivolatile compounds and might significantly alter both particle mass and composition as compared to a one-phase particle. We present a new liquid-liquid equilibrium and gas/particle partitioning model, using as a basis the group-contribution model AIOMFAC (Zuend et al., 2008). This model allows the reliable computation of the liquid-liquid coexistence curve (binodal), corresponding tie-lines, the limit of stability/metastability (spinodal), and further thermodynamic properties of multicomponent systems. Calculations for ternary and multicomponent alcohol/polyol-water-salt mixtures suggest that LLE are a prevalent feature of organic-inorganic aerosol systems. A six-component polyol-water-ammonium sulphate system is used to simulate effects of relative humidity (RH) and the presence of liquid-liquid phase separation on the gas/particle partitioning. RH, salt concentration, and hydrophilicity (water-solubility) are identified as key features in defining the region of a miscibility gap and govern the extent to which compound partitioning is affected by changes in RH. The model predicts that liquid-liquid phase separation can lead to either an increase or decrease in total particulate mass, depending on the overall composition of a system and the particle water content, which is related to the hydrophilicity of the different organic and inorganic compounds. Neglecting non-ideality and liquid-liquid phase separations by assuming an ideal mixture leads to an overestimation of the total particulate mass by up to 30% for the composition and RH range considered in the six-component system simulation. For simplified partitioning parametrizations, we suggest a modified definition of the effective saturation concentration, C_j^*, by including water and other inorganics in the absorbing phase. Such a C_j^* definition reduces the RH-dependency of the gas/particle partitioning of semivolatile organics in organic-inorganic aerosols by an order of magnitude as compared to the currently accepted definition, which considers the organic species only.

Additional Information

© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 4 May 2010; Published in Atmos. Chem. Phys. Discuss.: 12 May 2010; Revised: 17 August 2010; Accepted: 19 August 2010; Published: 24 August 2010. This work was supported by Swiss National Science Foundation (SNF) under project no. PA00P2 126227 and the Competence Center Environment and Sustainability of the ETH Domain (CCES) project IMBALANCE. This work was also supported by the Office of Science (BER), US Department of Energy Grant DE-FG02-05ER63983, by US Environmental Protection Agency STAR Research Assistance Agreement RD- 833749, and the Electric Power Research Institute. This work has not been formally reviewed by the EPA. The view expressed in this publication are solely those of the authors. Edited by: G. McFiggans.

Attached Files

Published - Zuend2010p11396Atmos_Chem_Phys.pdf


Files (5.5 MB)
Name Size Download all
5.5 MB Preview Download

Additional details

August 19, 2023
October 20, 2023