Junge-Pankow adsorption model

Filtration Sampling vs. Junge-Pankow Adsorption Model... 

Methods for Estimating the Particle/Gas Distribution in Ambient Air 10.3.1 Junge-Pankow Adsorption Model... 

Illustrative calculations appear below for estimating the particulate fraction (c()) of p,p -DDT in urban air at 20°C using the Junge-Pankow adsorption model (Equation 3), the Mackay adsorption model (Equation 15), and the octanol-air partition coefficient model (Equation 25). Table 10.3 lists values of P3 and Koafor p,p -DDT and other POPs of different chemical classes. All model calculations are for an urban air TSP = 80 pg/m3 (Shah et al., 1986). 

Figures 10.2 and 10.3 compare the particulate percentages obtained from the hi-vol sampling correlations in Table 10.2 with those estimated from the Junge-Pankow adsorption model (Equation 3). The model was applied using a value for c of 17.2 Pa-cm, surface area parameters (9, cm2 aerosol/cm3 air) of 6.3 x 106 for urban air, and 7.5 x 10-7 for rural (average background) air. These 9 values were scaled downward from those in Table 10.1, to adjust for the lower TSP concentrations, e.g., urban air = 1.1 x 10-5 (80/140) = 6.3 x 10-6 rural air = 1.5 x 10-6 (30/60) = 7.5 x 10-7. The fraction on aerosols (( >) was calculated from Kp and TSP by Equation 9.

As Chapter 10 discusses in detail, chemical compounds in the atmosphere are partitioned between the gas and particle phases (Pankow, 1987 Bidleman, 1988), and the phase in which a chemical exists in the atmosphere can significantly influence its dominant tropospheric removal process(es) and lifetime (Bidleman, 1988 Atkinson, 1996). Gas/particle partitioning has been conventionally described by the Junge-Pankow adsorption model that depends on the liquid-phase (or sub-cooled liquid-phase) vapor pressure, Pu at the ambient atmospheric temperature, the surface area of the particles per unit volume of air, 9, and the nature of the particles and of the chemical being adsorbed (Pankow, 1987 Bidleman, 1988). The fraction of the chemical present in the particle phase, ( ), depends on these parameters through an equation of the form (Pankow, 1987 Bidleman, 1988) ... 

Comparison of Junge-Pankow Adsorption and Koa-based Absorption Models... 

FIGURE 9.65 Observed percentages in the particle phase of PAHs (( ) N-E air ( ) S-W air), PCBs (( ) nonortho, ( ) monoortho, and multiortho PCBs, respectively), and ( ) PCNs in Chicago air compared to model predicted values, (a) Solid line is calculated with Junge-Pankow (J-P) adsorption model (Eq. (TT)). (b) Solid and dotted lines are calculated with absorption model for aerosols assumed to contain 10 and 20% organic matter (om), respectively (adapted from Harner and Bidleman, 1998). 

Despite many years of interest in the phase distribution of POPs, few predictive models are available. A Langmuir-type relationship, which Junge (1977) first proposed and Pankow (1987) later reviewed and critically evaluated, is the most popular model for estimating adsorption onto aerosols. The Junge-Pankow equation relates the fraction of particulate POPs (c >) to the saturation liquid-phase vapor pressure of the compound ( P Pa) and the surface area of particles per unit volume of air (8, cm2 aerosol / cm3 air). 

The 9-parameter is also subject to uncertainty. It is likely that Whitby s (1978) estimates of 9 (Table 10.1) do not reflect the true surface area distribution, since they were based on the average size spectrum of aerosols and assumed spherical particles. Adsorption/desorption kinetics (Kamens et al., 1995 Rounds and Pankow, 1990,1993) and relative humidity (Goss and Eisenreich, 1997 Lee and Tsai, 1994 Pankow et al., 1993 Storey et al., 1995 Thibodeaux et al., 1991) influence the adsorption of POPs onto aerosols, and the Junge-Pankow model does not take these factors into account. 

Comparison of Junge-Pankow and Mackay adsorption models (top) and Koa model (bottom) with observed particulate percentages ([Pg.274]

For adsorption mechanism, neglecting every process except adsorption was proposed by Junge (1977) (Junge 1977) and later critically reviewed by Pankow (1987) (Pankow 1987), the Junge-Pankow model (Eq. 2) is the most common method for estimating adsorption of SVOCs to aerosols and it can be simphhed as Eq. 3. 

The most widely used fractionation model (Eq. 13) is based on above mentioned adsorption mechanism. It was proposed by Junge (1977) and evaluated by Pankow (Pankow 1987 Bidleman 1988). 

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