Steady-State Mass Balance Model for Predicting Particle–Gas Concentration Ratios of PBDEs

Abstract

Assuming equilibrium partitioning between the gas and particle phases has been shown to overestimate the fraction of low-volatility chemicals in the particle phase. Here, we present a new steady-state mass balance model that includes separate compartments for fine and coarse aerosols and the gas phase and study its sensitivity to the input parameters. We apply the new model to investigate deviations from equilibrium partitioning by exploring model scenarios for seven generic aerosol scenarios representing different environments and different distributions of emissions as the gas phase, fine aerosol, and coarse aerosol. With 100% of emissions as the particle phase, the particle–gas concentration ratio in our model is similar to the equilibrium model, while differences are up to a factor of 10 6 with 100% of emissions as the gas phase. The particle–gas concentration ratios also depend on the particle size distributions and aerosol loadings in the different environmental scenarios. The new mass balance model can predict the particle–gas concentration ratio with more fidelity to measurements than equilibrium models. However, further laboratory-based evaluations and calibrations of the standard sampling techniques, field investigations with preferably size-resolved measurements of aerosol particle composition, together with the appropriate process modeling for low-volatility chemicals are warranted.

Molecular Dynamics Simulation Prediction of the Partitioning Constants (KH, Kiw, Kia) of 82 Legacy and Emerging Organic Contaminants at the Water–Air Interface

“…A key hindrance to the mitigation of organic contaminants (OCs) is insufficient knowledge of the thermodynamic constants that reflect their affinity for different phases and interfaces in natural and engineered systems. − This limited availability of fundamental thermodynamic data reflects a widening gap between, on the one hand, the ability of regulatory agencies to carry out experimental characterizations of substances that can be highly hazardous or challenging to synthesize and, on the other hand, the rapidly increasing diversity of OCs illustrated by the nearly 70 000 chemicals or mixtures registered globally in the past decade , or by the nearly 4000 applications for regulatory approval submitted to the US Environmental Protection Agency (EPA) between 2016 and 2021…”

Modeling Global Environmental Fate and Quantifying Global Source–Receptor Relationships of Short-, Medium-, and Long-Chain Chlorinated Paraffins

“…Moreover, the default assumptions of (i) equilibrium gas–particle partitioning and (ii) no degradation on atmospheric particles in BETR-Global can overestimate the atmospheric transport of CPs, especially for LCCPs, since they may not reach gas-particle partitioning equilibrium , and/or undergo multiphase reactions (albeit with possibly much slower rates , ). Our additional illustrative calculations with C 25 –CPs either applying steady-state gas-particle partitioning or allowing for degradation on particles (Figure S11) suggest that abandoning the default assumptions lowers atmospheric concentrations by less than an order of magnitude.…”

“…Our additional illustrative calculations with C 25 –CPs either applying steady-state gas-particle partitioning or allowing for degradation on particles (Figure S11) suggest that abandoning the default assumptions lowers atmospheric concentrations by less than an order of magnitude. Future global fate modeling efforts should seek to account for nonequilibrium partitioning (e.g., refs , ) and multiphase chemistry in the atmosphere. Finally, BETR-Global does not appropriately represent snow and ice, which is a limitation, especially for the Arctic and Antarctic regions.…”

Applications of the octanol–air partitioning ratio: a critical review

“…52,53 On the other hand, compounds with a log 10 K OA in excess of 13 are unlikely to achieve equilibrium with atmospheric particles within the atmospheric lifetime of most particles. 54…”