James F. Pankow

Review and comparative analysis of the theories on partitioning between the gas and aerosol particulate phases in the atmosphere

An analysis has been carried out of the different approaches used to describe partitioning between the gas and aerosol particulate phases. The equation of Junge (Fate of Pollutants in the Air and Water Environments, edited by I.H. Suffet, Part I, pp. 7–26, Wiley, New York, 1977) has been shown to be based on a linear Langmuir isotherm, and as such has been shown to be equivalent to the equation of Yamasaki et al. (Environ. Sci. Technol. 16, 189–194, 1982). Prior to this work, Bidleman and Foreman (The Chemistry of Aquatic Pollutants, edited by R.A. Hites and S.J. Eisenreich, ACS Advances in Chemistry Series, 1987) developed a parameterization describing an equivalence between these two equations that is applicable when the enthalpy of desorption (Q1) from the paniculate matter surface is similar to the enthalpy of vaporization (Qv) of the pure liquid compound. That parameterization is valid when ¦Q1- Qv¦ is significantly less than 1 kcal mole−1. A fundamental consideration of the process of gas/solid partitioning is used in this work to develop predictive equations for the value of the equilibrium constant KY = cg(TSPY)cp where cg and cp are the gas phase and paniculate phase-associated concentrations (ng m−3), respectively, and TSPY is the concentration of suspended paniculate matter (ng m−3). In particular, it is derived that for a given compound, log KY = −Q1(2.303 RT) + log [2.53 × 105 (MT)12/AtsptO] where R = gas constant, T = temperature, M = mol. wt, Atsp = specific surface area for the paniculate matter and t0 is a characteristic molecular vibration time. In terms of the vapor pressure po (torr) of a compound or series of compounds, KY = 1.6 × 104poNsAtspTexp [(Q1- Qv)RT] where Ns is the number of moles of sorption sites per cm2 of particulate matter surface area. When sorption to the surface is liquid-like (i.e. ¦Q1- Qv¦∼-0), then Ky = 1.6 × 104poNsAtspT

Trace organic compounds in rain—III. Particle scavenging of neutral organic compounds

Abstract Concurrent measurements were obtained for a number of neutral organic compounds associated with suspended particles in rain and in the atmosphere. Particle scavenging ratios (Wp) were determined and compared to gas scavenging ratios (Wg) obtained concurrently, in order to determine the relative importance of particle vs gas scavenging for organic compounds. The measured Wp values were much higher for polycylic aromatic hydrocarbons (PAHs) of molecular weight (MW) ⩽ 202, alkanes and phthalate esters than they were for PAHs of MW > 202. The Wp values ranged from 102 to 105 and averaged 14,000, a lower value than the 105–106 which has been measured for many inorganics. The low scavenging ratios are consistent with a below-cloud process for the particles containing these organic compounds. The compounds with relatively higher Wp values may be associated to a larger extent with large particles, which are more efficiently scavenged below-cloud. Due to the low Wp values found for most of the PAHs, particle scavenging was less important than gas scavenging for those compounds.

An evaluation of contaminant migration patterns at two waste disposal sites on fractured porous media in terms of the equivalent porous medium (EPM) model

Contamination has occurred many non-indurated and bedrock systems wherein the groundwater flows almost exclusively through a network of connected, open fractures. The matrix surrounding the fractures often possesses porosity which allows contaminant diffusion into the matrix. If the diffusion rates are fast relative to the fracture groundwater velocity, transport effects may be predicted by considering the system to be an equivalent porous medium (EPM). The rapidity with which fracture/immobile-matrix equilibrium is established will be determined in part by the: fracture aperture (2b); interfracture spacing (2B); porosity in the immobile matrix (θim); and the matrix diffusion coefficient (D′). Two systems which are characterized by very different values of the above parameters have been studied by our laboratories. At Alkali Lake, Oregon, the EPM approach describes contaminant transport well. At Bayview Park, Ontario, the EPM approach is not appropriate. Several features of the two sites are compared to illustrate the different nature of these two sites. These features include: (1) natural characteristics of the groundwater systems; (2) contaminant distributions; (3) observed transport; and (4) computed fracture/immobile-matrix diffusion times.

Adsorption-thermal desorption as a method for the determination of low levels of aqueous organics

Abstract Adsorption followed by thermal desorption (ATD) with Tenax GC is an effective analytical tool for the preconcentration-analysis of water samples containing μ/kg quantities of the three United States Environmental Protection Agency (U.S. EPA) “Priority Pollutants” p-dichlorobenzene, hexachloro-1,3-butadiene, and 2-chloronaphthalene. A centrifugation method allows the removal of all but 80 μl of water from a glass cartridge packed with 0.75 g Tenax GC. A 10-min follow-up vacuum-desiccation step will reduce the residual water to ≈ 5 μl. A new procedure is presented for conducting recovery tests with sparingly soluble compounds and for the desorption of loaded cartridges. The recovery efficiencies for the tree compounds showed little dependence upon the sample flow-rate in the range 0.25–2.0 ml/sec. One cartridge absorbed ≈ 80% of these compounds at all flow-rates, and a second cartridge in series recovered the remaining ≈ 20%.

The calculated effects of non-exchangeable material on the gas-particle distributions of organic compounds

Abstract The behavior of a chemical species in the atmosphere depends on how it partitions between the gas and aerosol particulate phases. Available evidence indicates that this partitioning can be described by a compound- and temperature-dependent constant K = A ( TSP )/ F , where A and F are the atmospheric concentrations measured in the gas and particulate phases, respectively (ng m −3 ). TSP is concentration (in μg m −3 ) of total suspended particulate matter. K values within some classes of compounds are known to correlate with the corresponding log p o values where p o is the vapor pressure of the compound. (For a solid compound, the vapor pressure of the sub-cooled liquid should be used.) Such correlations can break down when portions of the compounds are bound inside the particles. This paper develops equations for predicting the magnitude of this effect. The specific case of polycyclic aromatic hydrocarbons is used as an example. Values for log A ( TSP )/ F are predicted to be significantly undervalued in a variety of circumstances compared with what would be expected at full equilibrium, even when the fraction of non-exchangeable material is only a few per cent. Similarly, φ values [ = F /( A + F )] can be significantly overvalued. A knowledge of the magnitude of this effect will be necessary for accurate predictive modeling of the fates of chemical species in the atmosphere.

Effects of linear flow velocity and residence time on the retention of non-polar aqueous organic analytes by cartridges of tenax-gc

Abstract Strong evidence has been obtained which indicates that film diffusion controls the retention of non-polar organics of low aqueous solubility by the sorbent Tenax-GC. Model compounds which have been studied in this context include the four U.S. Environmental Protection Agency priority pollutants o-dichlorobenzene, 1,2,4-trichlorobenzene, napththalene, and hexachloro-1,3-butadiene. The data indicate that compounds such as these have large aqueous retention volumes on this sorbent. Once sorbed, little loss occurs for μg/l concentrations and sample volumes of several liters. Equations are developed which predict the percent recovery as a function of cartridge dimensions and sample volume flow rate.

Carbon Dioxide Transfer at the Gas/Water Interface as a Function of System Turbulence

For processes which are not rate limited by chemical reactions, interfacial mass transfer will be controlled by the fluid mixing. This applies to transfer across both the gas/water and the oil/water (e.g. petroleum spill) interfaces. As they involve environmental water bodies, such processes are therefore often controlled by the degree and nature of the turbulence underlying the interface. Efforts in our laboratories have been directed towards the use of the pH-dependent laser-induced fluorescence (LIF) of fluorescein compounds to characterize the mass transfer of CO2 (an acid) across both the gas/water interface and the oil/water interface. The photodiode monitoring of the LIF intensity in dilute fluorescein solutions (~10−7 M) as a function of depth allows the calculation of the CO2 flux across the interface as well as across any internal solution surface. Turbulence has been generated by means of an oscillating grid. Mass transfer measurements have been made under conditions of varying turbulence intensity, length scale, and distance to the interface.

Error magnitudes in extrapolated approximations of sorbent retention volumes obtained by using temperature-dependent vapor pressures

Abstract The temperature dependence of the vapor pressure of a compound can be used to obtain an estimate of the effects of temperature ( T , K) on the retention volume of that compound on sorbents used in gas sampling. Since the T -dependence of the vapor pressure depends on the enthalpy of vaporization ΔH v and not on the enthalpy of desorption ΔH s from the sorbent surface itself, such an estimate will be subject to error. Let T 2 be the temperature at which an estimate of the retention volume is desired, and let T 1 be the temperature at which the retention volume is known. The magnitude of the error will then increase as the magnitudes of ( T 2 − T 1 ) and ( ΔH s − ΔH v ) increase. If both ΔH s and ΔH v are independent of T over the range of interest, then the error will be zero when either ( T 2 − T 1 ) or ( ΔH s − ΔH v ) is zero.