Partitioning of SVOCs

Particularly relevant to the gas-partiele partitioning of SVOCs is the carbonaceous fraction of the partieles, ineluding organic matter (OM) as well as the elemental carbon (black carbon or soot). The weight fraction of OM, fau, is an important independent variable in the prediction of Kp for SVOCs. Soot particles are highly porous with large nonpolar surface areas, which render them high affinity for SVOCs, particularly those with planar molecular structures such as PAHs. 

The octanol/air partition coefficient, Koa, is the ratio of the solute concentration in n-octanol to that in air when the octanol-air system is at equilibrium. It is a key descriptor of the absorptive partitioning of SVOCs between the atmosphere and organic phases found in soil, in vegetation, and on aerosols. The application of Koa is based on the assumption that the interaction between the SVOCs and the environmental organic phases sufficiently resembles the interaction between the SVOCs and n-octanol. 

Usually, organic chemicals are associated with particles through two mechanisms adsorption onto aerosol surface and absorption into aerosol OM. Both mechanisms drive gas/particle partitioning of SVOCs. 

Gas-particle partitioning of SVOCs is an important process which influences their mobility and environmental fate. The knowledge of the gas-particle partitioning can help explain observed mobility, photolytic transformation, and removal from the atmosphere by dry and wet deposition. A great deal is yet to be learned, however, in order to quantitatively define the link of physicochemical properties to the overall environmental transport and fate. 

He, J. and R. Balasubramanian. 2009. A study of gas/particle partitioning of SVOCs in the tropical atmosphere of Southeast Asia. Afmoi. Environ. 43(29) 4375-4383. 

An important aspect with regard to the atmospheric fate of SVOCs is their partitioning between the gas and particle phases. Once released into the atmosphere, generally SVOCs would be partitioned in these two phases and reach a partitioning equilibrium according to temperature dependences and the vapor pressure of the chemicals (Pankow and Bidleman 1992 Cotham and Bidleman 1995). The particulate-bound SVOCs could be transferred from the atmosphere to... 

The behavior and fate of SVOCs in the atmosphere greatly depends on the distribution of compounds between different sub-compartments of the atmosphere such as atmospheric gaseous and particulate phases. It has been summarized that gas-particle partitioning is controlling the relative importance of different deposition pathways for SVOCs from the atmosphere to the terrestrial and aqueous surface (Bildleman 1988). 

Due to the observational evidence that submicron particles (non-filter retained particles) do exist in the filtrate and influence the partitioning behavior of SVOCs in rainwater (Gschwend and Wu 1985 Glotfelty et al. 1990). Equation 12 was modified considering the scavenging of submicron particles (Poster and Baker 1996a) ... 

In the aqueous environment, those SVOCs sorbed onto colloidal matter (DOC) are not available for air-water exchange. The partitioning between truly dissolved and colloidal phases has to be investigated in order to obtain the truly dissolved concentrations of SVOCs. The apparent dissolved concentrations (non-filter retained Ifaction) of SVOCs (cdissolved organic carbon, mg 1 ) phases, onto both of which the fractions of SVOCs partitioned can be estimated as described in Eq. 5 by Totten et al. (2001) and Wurl et al. (2006a)... 

The distribution of SVOCs between the gas and particle phases in air at equilibrium is commonly described by the particle-gas partition coefficient Kp (Pankow 1994) ... 

Liquid-liquid extraction (LLE) is the most common method for the isolation of SVOCs and nonvolatile compounds from water samples. It is based on the partitioning of analytes from an aqueous phase to a liquid organic phase. In LLE,... 

SVOCs may be simultaneously present in meaningful amounts in the gas phase and on the surface of airborne particles. Therefore it is important to sample both the gas phase and the partide phase. This distribution between the gas phase and particles is known as partitioning and may roughly be illustrated by Junge s equation (Junge, 1977) derived on the basis of adsorption theory ... 

Pesticides are either semivolatile or nonvolatile . For example, the boiling points of DDT (260 °C), lindane (around 320 °C) and pentachlorophenol (PCP) (around 310 °C) [8] classify these pesticides as semivolatile. SVOCs partition between air and house dust, whereas POM are exclusively found in house dust. Methods to analyze pesticides in indoor air (semivolatile pesticides) and in house dust (semivolatile and particle-bound pesticides as well as particulate pesticides), sources for their occurrence indoors, concentrations found in indoor environments as well as impacts are reviewed in this chapter. 

Therefore, dust and its associated fine particulate matter tend to become a sink for semi volatile organic compounds (SVOCs) (Butte and Heinzow 1994). Calculations suggest that many SVOCs have long indoor persistence, even after their primary sources have been removed. If the only removal mechanism is ventilation, moderately sorbing compounds (with octanol—air partition coefficients (K a) > 10 ) may persist indoors for hundreds to thousands of hours, while strongly sorbing compounds (Koa > 10 ) may persist for years (Weschler and Nazaroff 2008). 

Similar to the partitioning in the water column, SVOCs can also partition through an absorption process in addition to physical adsorption onto the surface of particles. SVOCs would dissolve in the organic matter (OM) in the atmosphere, which exists both as primary (POA) and as secondary organic aerosols (SOA) (Lohmann and Lammel 2004). Kqa absorption model has been proposed by Pankow (1994) and Finizio et al. (1997). The octanol-air partitioning coefficient (Kqa) can be used to predict Kp with the assumption that the predominant distribution process is absorption (Harner and Bidleman 1998). The relationship between Kp and Kqa is... 

As discussed above, SVOCs are removed from the atmosphere and transported to the waters by precipitation scavenging of atmospheric vapors and particles, which are incorporated into the rain within or below the clouds. After SVOCs are deposited into the bulk seawater, partitioning in water column can affect the distribution of pollutants between the dissolved aqueous and the solid phases and eventually impact the fate of these compounds in oceans (Luo et al. 2004). In addition, air-sea exchange can make SVOCs diffuse across the air-sea interface however, the sea surface microlayer (SML), a unique compartment at the air-sea boundary defined operationally as the upper millimeter (1-1,000 pm)... 

Kp is temperature dependent and log Kp has a linear relationship with the reciprocal of temperature log Kp = A/T — B, where A and B are constants that are specific to individual SVOCs (Yamasaki et al. 1982). Relative humidity also affects the particle-gas partitioning. Jang and Kamens concluded that humidity effect on partitioning was the most significant for hydrophobic compounds, such as PAHs, in polar particles (Jang and Kamens 1998). Pankow et al. found a significant negative linear correlation between relative humidity and log Kp for seven PAH compounds (Pankow et al. 1993). 

---