Analysis of the Dynamic Interaction Between SVOCs and Airborne Particles

Abstract

A proper quantitative understanding of the dynamic interaction between gas-phase semivolatile organic compounds (SVOCs) and airborne particles is important for human exposure assessment and risk evaluation. Questions regarding how to properly address gas/particle interactions have introduced uncertainty when predicting SVOC concentrations and assessing exposures to these compounds. In this study, we have developed a dimensionless description for the dynamic interaction between SVOCs and organic particles. A better criterion to judge whether the internal resistance (diffusion in and out of aerosols) is negligible compared with the external one (from bulk air to aerosol surfaces) is presented. The analysis is applicable regardless of the phase state of particles (either liquid or amorphous semisolid/solid). It is found that for both porous and nonporous particles, the internal resistance can be reasonably neglected for particles with diameters between 0.01 and 10 µm if the particulate organic matter is in the liquid phase. A lumped description therefore can be applied to determine, with greater accuracy than in previous studies, the timescale required to attain gas/particle equilibrium for such particles. The instantaneous equilibrium assumption is found to be reasonable for relatively volatile species such as pyrene, but not for the less volatile species such as di-(2-ethylhexyl)-phthalate (DEHP). For DEHP and 2.5 µm diameter particles, the instantaneous gas/particle equilibrium assumption can cause a two orders of magnitude error in the estimation of the gas-phase concentration and a factor of two error in the estimation of the particle-phase concentration.

Gas and particle size distributions of polychlorinated naphthalenes in the atmosphere of Beijing, China

“…This suggests that SPCNs may tend to adsorb onto finer PM. For the partitioning of organic pollutants between particles of different sizes, the absorption capacity of the particles is proportional to the organic content and surface area, which means that fine particles have higher mass transfer rates than larger particles (Li and Davis, 1996;Liu et al, 2013). Therefore, the enrichment of PCNs on fine particles (PM 1.0 or PM 2.5 ) could be attributed to their larger surface areas compared with larger particles.…”

Quantifying water diffusion in high-viscosity and glassy aqueous solutions using a Raman isotope tracer method

“…Several studies have suggested that atmospheric aerosol particles are not in equilibrium with surrounding gas phase compounds (Roth et al, 2005;Perraud et al, 2012;Abramson et al, 2013), which may lead to errors in the evaluation of particle-phase and gas-phase concentrations (Liu et al, 2012;Shiraiwa and Seinfeld, 2012;Shiraiwa et al, 2013). The phase of an aerosol particle has been found to affect reactivity (Knopf et al, 2005;Kuwata and Martin, 2012), and the chemical lifetimes of condensed organics can be significantly increased if diffusion is limited (Shiraiwa et al, 2010Pfrang et al, 2011).…”

Pivotal Roles of Metal Oxides in the Formation of Environmentally Persistent Free Radicals

“…16 EPFRs attach more easily to fine particles than coarse particles because fine particles have large surface areas and porous surfaces. 17 To date, even though it has been reported that nanoparticles are largely retained on solid waste combustion residues in full-scale incinerators and in metal smelting processes, 18−20 the effect of metal oxide particle size on EPFR formation has not been evaluated. Nanoparticles of various oxides are ubiquitous in the atmosphere because of their widespread use in various applications, such as electronic devices, cosmetics, food additives, and medicine.…”