GAS-PARTICLE DISTRIBUTION OF SEMIVOLATILE ORGANICS

In short, understanding the gas-particle partitioning of SOC is important in a number of areas in atmospheric chemistry as well as related aspects of toxicology. 

The earliest work in this area assumed that particles in the atmosphere were solid and that the uptake of SOC involved adsorption to a solid or solid-like surface. It was subsequently recognized that many atmospheric particles are liquid or have liquid-like outer layers, and hence the uptake of gases could be treated as absorption into a liquid. These approaches are summarized in the following. It should be noted that these treat the equilibria between the gas- and condensed-phase species i.e., it is assumed that thermodynamics rather than kinetics controls the distribution between the phases. The implications of this assumption are discussed later. 

Given these caveats, we first treat the case of adsorption to a solid surface, and then absorption into a liquid particle or liquid surface layer on a particle. As we shall see, the distribution of SOC between the gas and condensed phases can be used to infer the nature of the sorbent sites. 

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Many persistent organic pollutants (POPs) are semivolatile compounds which undergo exchange between air and atmospheric particles, soils, and vegetation. Classes of POPs include polychlorinated biphenyls (PCBs), pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs, PCDFs). The distribution of these substances between the particle and gas phases in the atmosphere is a... 

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