Gas/particle partitioning

Li YM, Jiang GB, Wang YW, Wang P, Zhang QH (2008) Concentrations, profiles and gas-particle partitioning of PCDD/Fs, PCBs and PBDEs in the ambient air of an e-waste dismantling area, southeast China. Chin Sci Bull 53(4) 521-528. doi 10.1007/sl 1434-008-0125-8... 

Dachs, J., Eisenreich, S.J. (2000) Adsorption onto aerosol soot carbon dominates gas-particle partitioning of polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 34, 3690-3697. 

Kaupp, K., McLachlan, M.S. (1999) Gas/particle partitioning of PCDDs/Fs, PCBs, PCNs and PAHs. Chemosphere 38, 3411-3421. 

Pankow JF (2001) A consideration of the role of gas/particle partitioning in the deposition of nicotine and other tobacco smoke compounds in the respiratory tract. Chem Res Toxicol 14(11) 1465-1481... 

Odabasi, M., Cetin, B., and Sofuoglu, A. Henry s law constant, octanol-air partition coefficient and subcooled liquid vapor pressure of carbazole as a function of temperature Application to gas/particle partitioning in the atmosphere, Chemosphere, 62(7) 1087-1096, 2006. 

Liang C, Pankow JF (1996) Gas/particle partitioning of organic compounds to enviromnental tobacco smoke partition coefficient measurements by desorption and comparison to urban particulate material. Environ Sci Technol 30 2800-2805... 

Pankow, J. F., An Absorption Model of Gas/Particle Partitioning of Organic Compounds in the Atmosphere, Atmos. Environ., 28, 185-188 (1994a). 

Care must be taken in extrapolating the results of laboratory studies to the lower concentrations and generally higher relative humidities (RH) found in ambient air. For example, Izumi et al. (1988) showed that the organic aerosol yield for the cyclohexene-03 reaction decreased in a nonlinear fashion as the initial reactant concentrations decreased from 5 ppm in addition, the concentration of condensation nuclei increased steeply with RH above 30%. This may be at least in part due to the effects of gas-particle partitioning on the measured aerosol yields discussed in more detail below. 

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. 

A gas-particle partition coefficient, Kp, is commonly used to describe the distribution of a SOC between the gas and particle phase. It is defined as the ratio of the SOC in particles (in units such as ng pg 1) to that in the gas phase (in units such as ng m 3). In essence, it is the fraction of the mass of total suspended particulate matter (TSP) that is the SOC of interest divided by the SOC gas-phase concentration. This gas-particle partition coefficient, which has units of m3 pig, can be calculated from the following ... 

In short, the form of the gas-particle partitioning defined in Eq. (MM) is consistent with Langmuir adsorption of the SOC on the surface of the TSP. 

Figure 9.61 shows some typical plots to test Eq. (VV) for some SOC in the form of higher molecular weight alkanes and some PAH (see Chapter 10) at various relative humidities (Storey et al., 1995). In this case, the gas-particle partitioning coefficient Kp has been normalized to take into account different surface areas by using a surface area normalized coefficient, Kp s, defined as... 

However, it is also the case that slopes different from mr 1 can occur even under equilibrium conditions, due to the nature of the molecular interactions involved in adsorption on a surface. For example, Goss and Schwarzenbach (1998) propose a modified formulation of Eq. (VV) that more explicitly takes into account the interactions between the SOC and the surface on a molecular level. Thus, based on work by Goss (1997), they express the relationship between a gas-particle partition coefficient K fds, defined as the adsorbed con-... 

This formulation explicitly accounts for both the properties of the surface and those of the adsorbing SOC that determine on a molecular level the amount of adsorption of the gas on the surface, and hence the gas-particle partitioning. For example, Goss and Schwarzenbach (1998) describe the implications of three... 

FIGURE 9.61 Surface area normalized gas-particle partition coefficients as a function of liquid vapor pressure for some alkanes and PAHs on urban particulate matter (UPM) and quartz fiber filters (QFF) at 30% RH and 70% RH (adapted from Storey et al., 1995 data for UPM from Yamasaki el al. (1982) and Foreman and Bidle-nian (1990)). 

In short, the slope of plots of the natural logarithm of the gas-particle partitioning coefficient against In pL for a series of adsorbing SOC and surfaces can help to elucidate on a molecular level the types of interactions between the two. 

As discussed by Bidleman (1988), there is a variety of evidence from both laboratory and field studies that the gas-particle partitioning in many cases in the atmosphere is consistent with partitioning to a liquid rather than adsorption on a solid i.e., the gaseous SOC is absorbed into a liquid particle or a liquid on the surface of a solid. For example, tetrachlorodibenzo-p-dioxin (TCDD) is found in both the vapor and particle phases, whereas none would be found in the gas phase... 

If an SOC is absorbed into a liquid organic layer on the particle, a relationship between Kp and pL that is similar to that developed for adsorption onto a solid can be derived (Pankow et al., 1994a, 1994b). In this case, the gas-particle partitioning coefficient for the / th compound is defined as... 

The expression for the gas-particle partitioning coefficient Kp given by Eq. (DDD) in units of m3 per p.g is developed by Pankow (1994a, 1994b) as... 

Goss and Schwarzenbach (1998) define a unitless gas-particle partitioning coefficient, X, as the ratio of molar concentrations in the condensed, om, phase (c, om) to that in the gas phase (c, ). They show that using Eq. (HHH), Ki can be given by... 

FIGURE 9.63 Plots of om-phase-normalized gas-particle partitioning constant log Kp iun vs logarithm of the subcooled liquid vapor pressure, log pL, for a series of semivolatile PAHs partitioning on ( ) dioctyl phthalate (DOP) or (a) secondary organic aerosol (SOA) from photooxidized gasoline vapor. PAHs are as follows naphthalene, A acenaphthalene, B fluorene, C and C phenanthrene, D and D anthracene, E and E fluoranthene, F and F pyrene, G and G chrysene, H (adapted from Liang el al., 1997). 

In short, data such as those in Figs. 9.64 and 9.65 support the use of the octanol-air partitioning coefficient as a useful parameter for characterizing gas-particle partitioning of SOC into liquid particles or liquid layers on particles in air. 

This discussion of gas-particle partitioning has focused on the idea that equilibrium between the two phases is attained in the atmosphere. However, it should be noted that equilibrium cannot always be assumed in the atmosphere. For example, Wania et al. (1998) ex-... 

Bowman, F. M., J. R. Odum, J. H. Seinfeld, and S. N. Pandis, Mathematical Model for Gas-Particle Partitioning of Secondary Organic Aerosols, Atmos. Environ., 31, 3921-3931 (1997). 

Pankow, J. F., J. M. E. Storey, and H. Yamasaki, Effects of Relative Humidity on Gas Particle Partitioning of Semivolatile Organic Compounds to Urban Particulate Matter, Environ. Sci. Technol., 27, 2220-2226 (1993). 

Values recommended by Mackay et al. (1992) and Mackay and Callcott (1998) for the vapor pressures of a number of PAHs of atmospheric interest and several properties used in theoretical calculations of their gas-particle partitioning in ambient air are given in Table 10.6 for examples of their use, see discussion of gas-particle partitioning theory in Chapter 9.D and references cited above. 

Gas - Particle Partitioning, Sampling Techniques, and Ambient Levels of Selected PAHs and PACs... 

Gas-particle partitioning is also impacted by changes in ambient temperature and aerosol concentrations during sampling, resulting in artifacts in the relative particle- and gas-phase concentrations (see Hart and Pankow, 1994). 

A sampling system designed to reduce artifact problems was employed by Liang and co-workers (1997) in an experimental chamber study of the gas-particle partitioning of several PAHs (and //-alkanes) on three types of model aerosols and ambient urban particulate matter. The system consisted of a dual glass fiber filter system as described by Hart and Pankow (1994), followed by two parallel sampling trains for trapping... 

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