A wind tunnel study of dense gas dispersion in a stable boundary layer over a rough surface

Measurements of the vertical entrainment velocity into two-dimensional dense gas plumes over fully rough surfaces were carried out as part of a co-operative research programme with wind tunnel facilities in the USA. This paper presents results obtained for stable boundary layer conditions in the EnFlo wind tunnel at the University of Surrey; a companion paper treats the neutral boundary layer case. Mean velocity and temperature, turbulent normal and shear tresses, temperature fluctuations and heat fluxes were measured and used to demonstrate that a moderately stable atmospheric boundary layer had been successfully simulated in the tunnel. Entrainment velocities, W_E, were then deduced from the streamwise development of the concentration field, non-dimensionalised with respect to the friction velocity in the undisturbed flow, u^*, and correlated with the plume Richardson number, Ri^*. Higher non-dimensional entrainment speeds, W_E/u^*, were observed for Ri^*>5 in the stable boundary layer than in the neutral boundary layer, the difference growing with increasing Richardson number. Emission velocity ratios, W₀/u^*, were however larger in the stable experiments, and exceeded one at about Ri^*=18. Entrainment in the stable boundary layer appeared therefore to be more sensitive to emission velocity ratio than in the neutral case. Entrainment behaviour for Ri^*⩽5 followed that found in the neutral boundary layer. In this regime, use of the neutral boundary layer entrainment speed correlation is unlikely to lead to the over-prediction of plume dilution rates in moderately stable boundary layers.     

Wind-tunnel study of entrainment in two-dimensional dense-gas plumes at the EPA's fluid modeling facility

This wind-tunnel study has been conducted as part of a collaborative effort to investigate the effect of large surface roughness on the entrainment of air from a neutrally stable simulated atmospheric boundary layer into a continuous dense-gas plume. The present study examined the entrainment rates of dense-gas plumes as they were transported over two surfaces with similar geometry but significantly different roughness lengths (factor of 6). Extensive measurements of the flow and plume structures over a wide range of source Richardson numbers (Ri*) are reported. Carbon dioxide was released from a two-dimensional source in order to obtain a plume with virtually constant Ri*. Over the small roughness, the plume depths were generally large compared with the element heights, whereas over the large roughness, plume depths were comparable with the element heights. Retardation of mean velocities in the lower levels of the dense plumes (with compensating increases in the upper levels) was observed, as well as strong suppression of turbulence over quite large fractions of the boundary-layer depth. These effects increased as Ri* increased. Propagation of dense gas was observed upstream of the source due to gravity spreading. The flow within the plumes was observed to become laminar at the larger Ri*. The primary measurements comprised longitudinal surface concentration profiles. Where the plumes were fully turbulent, the plots of inverse concentration versus downwind distance formed reasonably straight lines. The sought-after entrainment velocities are proportional to the slopes of these lines and were found to diminish quite rapidly with Ri*. More in-depth analyses and intercomparisons with the results of the other laboratories are contained in a companion paper in this same volume (Briggs et al., 2001, Atmospheric Environment 35, 2265–2284).     

Unsteady characteristics of the dispersion process in the vicinity of a pig barn. Wind tunnel experiments and comparison with field data

Two complementary methods, field experiments and physical modelling in a wind tunnel, have been used to investigate the dispersion of tracer-gas released from the ventilation system of a pig barn, under near-neutral stability conditions. In both cases, concentration fluctuations were measured and the deduced statistical results were compared. The choice of data processing applied to the time series of concentration was motivated by special issues in the assessment of odour annoyances: “where, how often, how long and how strong does it smell?” These features were described by the mean concentration distribution, the intermittency factor, the persistence and the 90-percentile. The good agreement between field and wind tunnel data confirmed the ability to replicate in wind tunnel the unsteady properties of a dispersion process, if the unsteady turbulent behaviour of the atmospheric boundary layer was properly modelled.A parametrical study of the influence on the dispersion process of the ratio between the exhaust velocity from the stack and the wind speed was then performed in wind tunnel. The fundamental outcome was that the near-field dispersion process under neutral stability conditions, despite the strong influence of the building wake, was for the most part driven by the meandering behaviour of the plume and not so much by the diffusion process.This study was also focused on the influence of the averaging time on the statistical results. The scatter generated by using dimensionless averaging times 200<T_a^*<400 (used during field experiments) instead of T_a^*→∞ (averaging time to ensure reproducible statistic results) was quantified in the wind tunnel. A degree of representativity of the results obtained from short-term samples, compared to fully converged statistical results was therefore assessed.     

Validation of ADMS against wind tunnel data of dispersion from chemical warehouse fires

Comparisons are presented of the predictions of the atmospheric dispersion modelling system (ADMS) and wind tunnel data for plume dispersion from chemical warehouse fires. The focus of the comparisons is dispersion from structurally intact buildings with open roofs and dispersion of plumes flush with the ground without obstacles, however, dispersion from building shells and doors is also considered. Both buoyancy driven and momentum driven flows are treated, although emphasis is on buoyancy driven flows as these are generally more likely to occur in warehouse fires. The study shows that the ADMS building module is able to reproduce many of the features of dispersion observed in the wind tunnel. These include a recirculating region behind the building in which material may be trapped, a main wake which brings material down towards the surface, and appropriate sensitivity to the buoyancy and momentum of the emitted material, and the location of sources on the building roof. The comparisons suggest that the ADMS building model can be used to predict dispersion from the stages of fire development studied. The precise level of agreement depends (but not in a systematic way) on the buoyancy flux parameter F_B, the momentum flux parameter F_M and the number of roof lights. There are some significant differences between the wind tunnel boundary layer and the simulated atmospheric boundary layer in ADMS which have to be considered when making wind tunnel model comparisons. These relate mainly to the near surface where the wind tunnel underestimates turbulent velocities, the boundary layer height which in the wind tunnel corresponds to an atmospheric boundary layer depth of 82.5 m (atmospheric boundary layers are frequently an order of magnitude deeper), and the boundary layer top where the ADMS boundary layer is capped by an inversion and has low turbulence levels whereas the wind tunnel boundary layer has higher levels of turbulence and no capping inversion.     

Estimating micrometeorological inputs for modeling dispersion in urban areas during stable conditions

We examine the performance of three methods to estimate the surface friction velocity and the Monin–Obukhov (MO) length in stable conditions. Estimates from these methods are compared with measurements made at two urban sites: the Wilmington site located in the middle of an urban area, and the VTMX site located on a sloping, smooth area in Salt Lake City. The first method uses the mean wind at a single height (Single U or SU), the second uses the wind speed at a single level and the temperature difference between two levels (U delta T or UDT), and the third method uses two levels of wind speed and temperature (delta U delta T or DUDT). The performance of the SU and UDT methods in estimating u_* are comparable. The SU method yields better estimates of the MO length than the UDT method does. The DUDT method performs poorly in estimating both u_* and L. The major conclusions of this study are that (1) measurements of mean winds and temperatures at one or two levels at an urban location can provide adequate estimates of micrometeorological variables required in modeling dispersion in the stable boundary layer, and (2) methods based on using differences in temperatures and velocities between two levels can provide unreliable estimates of these variables because these differences can be overwhelmed by inevitable uncertainties in the measurement of mean variables.     

A numerical study of interacting buoyant cooling-tower plumes

The compact design of mechanical cooling towers necessitates that the plumes are issued into the cross-wind in close proximity. An improved understanding of the interaction of adjacent plumes is therefore required for better design of such cooling towers, which may lead to a reduction in their environmental impact. This paper presents the results of a numerical investigation into the interaction of two adjacent plumes in a cross-flow. The numerical model simulates small-scale wind tunnel experiments of a cooling tower arrangement. The computations are performed for three-dimensional, turbulent, buoyant and interacting plumes, and for a single plume for comparison. Two double-source arrangements, namely, tandem and side-by-side, with respect to the oncoming atmospheric boundary layer are considered. A low Reynolds number k–ε turbulence model is used with two discretisation schemes, hybrid and QUICK, and the results are compared. Comparisons are also made with the experimental results. The results show that the interaction of side-by-side plumes is dominated by the interaction of the rotating vortex pairs within the plumes. A tandem source arrangement leads to early merging and efficient rise enhancement. Comparisons of the predicted results with experimental data show good agreement for the plume rise.     

Numerical modeling on air quality in an urban environment with changes of the aspect ratio and wind direction

Due to heavy traffic emissions within an urban environment, air quality during the last decade becomes worse year by year and hazard to public health. In the present work, numerical modeling of flow and dispersion of gaseous emissions from vehicle exhaust in a street canyon were investigated under changes of the aspect ratio and wind direction. The three-dimensional flow and dispersion of gaseous pollutants were modeled using a computational fluid dynamics (CFD) model which was numerically solved using Reynolds-averaged Navier–Stokes (RANS) equations. The diffusion flow field in the atmospheric boundary layer within the street canyon was studied for different aspect ratios (W/H?=?1/2, 3/4, and 1) and wind directions (θ?=?90°, 112.5°, 135°, and 157.5°). The numerical models were validated against wind tunnel results to optimize the turbulence model. The numerical results agreed well with the wind tunnel results. The simulation demonstrated that the minimum concentration at the human respiration height within the street canyon was on the windward side for aspect ratios W/H?=?1/2 and 1 and wind directions θ?=?112.5°, 135°, and 157.5°. The pollutant concentration level decreases as the wind direction and aspect ratio increase. The wind velocity and turbulence intensity increase as the aspect ratio and wind direction increase.     

Concentration field and turbulent fluxes during the mixing of two buoyant plumes

In this work an experimental study of mixing of two identical plumes, carried out in a turbulent neutral boundary layer generated in a wind tunnel, is presented. Measurements have been performed with fast flame ionisation detectors (FFIDs) and a two-component Laser-Doppler Anemometer system. Results allow the study of both the average and the fluctuating concentration field, including the turbulent vertical and longitudinal mass fluxes, in single plumes and during the interaction of two identical plumes. This information gives insight into the details of the mixing phase of the two plumes. Results of trajectories and additional rise (due to plume interactions) have been compared with previous measurements carried out in laminar cross-flows, showing similar behaviour. Concentration distributions in plume cross-sections in turbulent cross-flows differ from those measured in laminar cross-flows. Average vertical and longitudinal velocity measurements into the plume core show the strength of the shielding effect of the upwind plume and some details of interaction between the counter-rotating vortex pairs (CVPs). For large values of the alignment angle φ, between the line joining the stacks and the cross-flow, an average negative vertical velocity is measured in the middle of the plume even if its centre of mass is rising. This downward velocity is induced by the slow interaction of the CVPs and generates a vertical stretching of the plume and negative rise enhancement. Vertical turbulent fluxes change sign on the plume centreline and are of opposite sign with respect to the longitudinal turbulent fluxes. Results indicate a good linearity between vertical turbulent fluxes and concentration gradients, with different proportionality for the top and bottom parts of the plume (especially in the near field) indicating that dispersion could be described by a gradient-transfer model.     

Wind tunnel study of air entrainment into two-dimensional dense gas plumes at the Chemical Hazards Research Center

Experiments in a neutrally stable wind tunnel boundary layer were made for two-dimensional (quasi-line) sources of carbon dioxide dispersing over two types of uniformly spaced (billboard) surface roughness elements. Velocity and concentration measurements were made with each surface roughness over a wide range of source Richardson number by varying carbon dioxide release rate and wind speed. Concentration measurements were made with a FID gas analyzer using an ethane tracer in the source gas, and velocity measurements were made with independent LDV and HWA systems. For each surface roughness, this paper describes the wind tunnel boundary layer and presents alongwind and vertical concentration profiles in the gas plume. Vertical velocity and concentration profiles were measured at selected downwind distances, and the profiles were integrated to confirm the consistency of the measurements with the mass of carbon dioxide released. The data are intended for development of improved vertical turbulent entrainment correlations for use in dense gas dispersion models applied to hazardous chemical consequence analyses.     

Fumigation of pollutants in and above the entrainment zone into a growing convective boundary layer: a large-eddy simulation

Fumigation of a passive plume located in or above the entrainment zone (EZ) into a growing convective boundary layer (CBL) has been simulated by large-eddy simulation (LES). Three non-dimensional parameters, α(=w_e0/w_*0), z₀/z_i0, and σ_z0/z_i0, are used to classify different cases, where w_*0 is the convective velocity scale, w_e0 the initial entrainment velocity, z_i0 the initial CBL height, z₀ the initial plume height, and σ_z0 is the initial plume half-depth. Forty cases have been run and analysed. The crosswind-integrated concentrations have been compared with existing laboratory data from a saline convection tank. The results show that LES is a promising tool to reproduce fumigation processes. With a relatively coarse grid mesh near the EZ, LES derives reliable results that are in a good agreement with the laboratory data. The first parameter, α, containing the effects due to inversion strength, plays an important role in determining C₀(T), the ground-level concentration (GLC) as a function of dimensionless time, T. For large α (say >0.03, corresponding to fast entrainment), variation of α gives significant change in C₀(T); whereas for a wide range of α between 0.01 and 0.02 (corresponding to slow entrainment), C₀(T) is almost independent of α. The starting time of fumigation does not vary significantly with the second parameter, z₀/z_i0 (relative height of plume), although C₀(T) is, in general, smaller for a higher plume. This confirms laboratory findings that the traditional notion of zero fumigation for a high plume (say above 1.10z_i) is not correct. The effect of the third parameter, σ_z0/z_i0, is on the magnitude of C₀(T); thinner initial plumes have higher GLCs.     

A Theory of Plume Rise Compared with Field Observations

A theory for the rise of a plume in a horizontal wind is proposed in which it is assumed that, for some distance downwind of a high stack, the effects of atmospheric turbulence may be ignored in comparison with the effects of turbulence generated by the plume. The theory, an extension of the local similarity ideas used by Morton, Taylor, and Turner,¹ has two empirical parameters which measure the rate that surrounding fluid is entrained into the plume. Laboratory measurements of buoyant plume motion in laminar unstratified cross flow are used to estimate the empirical parameters. Using this determination of the parameters in the theory, the trajectories of atmospheric plumes may be predicted. To make such a prediction, the observed wind velocity and temperature as functions of altitude, and flow conditions at the stack orifice, are used in numerically integrating the equations. The resulting trajectories are compared with photographs, made by Leavitt, et al.,² of TVA, of plumes from 500 to 600 ft high stacks. Within 10 stack heights downwind of the stack, the root mean square discrepancy between the observed height of the trajectory above ground level and the theoretical value is 14%, which is about the uncertainty in the observed height. The maximum plume rise within the field of observation is within 15% of that predicted by the present theory.     

The NOAA Twin Otter and its role in BRACE: A comparison of aircraft and surface trace gas measurements

A DeHavilland DHC-6 Twin Otter, operated by the National Oceanic and Atmospheric Administration, was deployed in Tampa, FL to measure aerosols and primary and secondary trace gases in support of the Bay Regional Atmospheric Chemistry Experiment (BRACE). The Twin Otter repeatedly overflew the surface chemistry monitoring super site near Sydney, FL to assess the comparability of surface and airborne datasets and the spatial representativeness of the surface measurements. Prior to comparing the chemical datasets, we evaluated the comparability of the standards used to calibrate surface and airborne detectors, as well as the uniformity of wind fields aloft and at the surface. Under easterly flow, when the dearth of significant upwind emission sources promoted chemical homogeneity at Sydney, trace gas concentrations at the surface and aloft were generally well correlated; R² ranged from 0.4396 for H₂O₂ to 0.9738 for O₃, and was typically better than 0.70 for NO, NO₂, NO_Y, HNO₃, HCHO, and SO₂. Mean ratios of aircraft-to-surface concentrations during 10 overflights of Sydney were as follows: 1.002±0.265 (NO), 0.948±0.183 (NO₂), 1.010±0.214 (NO_Y), 0.941±0.263 (HCHO), and 0.952±0.046 (O₃). Poorer agreement and larger variability in measured ratios were noted for SO₂ (1.764±0.559), HNO₃ (1.291±0.391), and H₂O₂ (1.200±0.657). Under easterly flow, surface measurements at Sydney were representative of conditions over horizontal scales as large as 50 km and agreed well with airborne values throughout the depth of the turbulently mixed boundary layer at mid-day. Westerly flow advected the Tampa urban plume over the site; under these conditions, as well as during transitional periods associated with the development of the land–sea breeze, surface conditions were representative of smaller spatial scales. Finally, we estimate possible errors in future measurement-model comparisons likely to arise from fine scale (or subgrid;<2 km) variability of trace gas concentrations. Large subgrid variations in concentration fields were observed downwind of large emission point sources, and persisted across multiple model grid cells (distances>4 km) in coherent plumes. Variability at the edges of the well-mixed urban plume, and at the interface of the land–sea breeze circulation, was significantly smaller. This suggests that even a failure of modeled wind fields to resolve the sea breeze return can induce moderate, but not overwhelming, errors in simulated concentration fields and dependent chemical processes.     

Monte Carlo simulation of nitrogen oxides dispersion from a vehicular exhaust plume and its sensitivity studies

The pollutant dispersion behavior from the vehicular exhaust plume has a direct impact on human health, particularly to the drivers, bicyclists, motorcyclists, pedestrians, people working nearby and vehicle passengers. A two-dimensional pollutant dispersion numerical model was developed based on the joint-scalar probability density function (PDF) approach coupled with a k–ε turbulence model to simulate the initial dispersion process of nitrogen oxides, temperature and flow velocity distributions from a vehicular exhaust plume. A Monte Carlo algorithm was used to solve the PDF transport equations in order to obtain the dispersion distribution of nitrogen oxides concentration. The model was then validated by a series of sensitivity experimental studies in order to assess the effects of vehicular exhaust tailpipe velocities, wind speeds and chemistry on the initial dispersion of NO and NO₂ mass concentrations from the vehicular exhaust plume. The results show that the mass concentrations of nitrogen oxides decrease along the centerline of the vehicular exhaust plume in the downstream distance. The dispersion process can be enhanced when the vehicular exhaust tailpipe velocity is much larger than the wind speed. The oxidation reaction of NO plays an important role when the wind speed is large and the vehicular exhaust exit velocity is small, which leads to chemical reduction of NO, and the formation and accumulation of NO₂ in the exhaust plume. It is also found that the effect of vehicular exhaust-induced turbulence in the vicinity of the exhaust tailpipe exit is more dominant than the effect of wind turbulence, while the wind turbulence gradually shows a significant role for the dispersion of nitrogen oxides along with the development of exhaust plume. The range of dispersion of nitrogen oxides in the radial direction is increased along with the development of vehicular exhaust plume.     

Wind tunnel experiment of tracer gas diffusion within unstable boundary layer over coastal region

A wind tunnel experiment was carried out to simulate stack gas diffusion within an unstable atmospheric boundary layer over a coastal region. The wind tunnel floor, 4 m leeward of the entrance of the test section, was heated to 90°C over a length of 6 m in the streamwise direction, and wind tunnel experiments were performed under the flat plate condition with a prototype-to-model length scale ratio of 1200. Three similarity criteria of flow fields in the wind tunnel and in atmosphere, viz., bulk Richardson number, surface Reynolds number and the ratio of the Peclet number to the Richardson number, were considered in the wind tunnel experiment. Tracer gas was released along the coastline at a height of 10 cm, which corresponded to 120 m in height in atmosphere. The obtained wind tunnel experimental results of ground level concentration were compared with 30-min average values of the field experiments, viz., the data from the Tokai 82 field experiment. The maximum ground level concentration and its location were accurately simulated when there was close similarity between the wind tunnel and atmospheric flow conditions. The maximum concentration increased and occurred closer to the source when the level of convection was relatively stronger in atmosphere.     

Groundwater munition residues and nitrate near Grand Island,Nebraska, U.S.A.

Munition residues from waste disposal on ordnance property have resulted in a defined plume of RDX contaminated groundwater stretching 6.5 km and underlying an area of 6.5 km². A smaller plume of TNT was detected near the plant's boundary. The relative positions of the plumes combined with an historical review of total plant output of RDX and TNT indicates that RDX is much more persistent than TNT. The estimated RDX transport velocity of 0.5 m day⁻¹ closely approximates the calculated Darcian velocity. The RDX plume sinks with recharge at a rate of about 0.5 m yr⁻¹.Nitrate is associated primarily with adjacent upgradient landuse and is not related to plant manufacture of ammonium nitrate. The average δ¹⁵N of the Nitrate was about + 10% and strongly suggests that animal wastes are the predominant source.     

Applied dispersion modelling based on meteorological scaling parameters

A method for calculating the dispersion of plumes in the atmospheric boundary layer is presented. The method is easy to use on a routine basis. The inputs to the method are fundamental meteorological parameters, which act as distinct scaling parameters for the turbulence. The atmospheric boundary layer is divided into a number of regimes. For each scaling regime we suggest models for the dispersion in the vertical direction. The models directly give the crosswind-integrated concentrations at the ground, x_y, for nonbuoyant releases from a continuous point source. Generally the vertical concentration profile is proposed to be other than Gaussian. The lateral concentration profile is always assumed to be Gaussian, and models for determining the lateral spread σ_y are proposed. The method is limited to horizontally homogeneous conditions and travel distances less than 10km. The method is evaluated against independent tracer experiments over land. The overall agreement between measurements and predictions is very good and better than that found with the traditional Gaussian plume model.     

A Correlation of Field Observations of Plume Rise

Data from 137 sets of plume observations, comprising nearly 1 500 data points, are correlated with two simple formulae. These formulae, one for the buoyancy-dominated rise region and the other for the stratification-dominated levelled-off region of a plume, represent an approximate form of the entrainment theory of Hoult, et al. (1968)¹ for the case of uniform atmospheric stratification and zero wind shear. The observations, which are those of the Tennessee Valley Authority and of Bringfelt (1968),⁶ were made of plumes whose source strengths ranged from 0.4 to 111 Mw and which were emitted from stacks of heights between 21 and 183 m. The two formulae are found to correlate the data equally well over all values of the stack exit and meteorological parameters, provided only that the bulk mean velocity of the stack gases exceeds the mean wind speed by at least 20%. The ratio of observed to calculated plume rise is found to be distributed log normally about the mean value.

The median rise at large distances downstream was found to differ insignificantly from that given by the effective stack height formula recommended recently¹¹ for large buoyant plumes. Based upon the correlation, two formulae are recommended for computing median plume rise at all distances downstream of the stack. The formulae include an estimate of the expected uncertainty in the predicted rise.     

A Lagrangian stochastic model for predicting concentration fluctuations in urban areas

A combined Lagrangian stochastic model with a micromixing sub-model is used to estimate the fluctuating concentrations observed in two wind tunnel experiments. The Lagrangian stochastic model allows fluid trajectories to be simulated in the inhomogeneous flow, while the mixing model accounts for the dissipation of fluctuations using the interaction by exchange with the mean (IEM) mechanism. The model is first tested against the open terrain, wind tunnel data of Fackrell, J.E. and Robins, A.E. [1982. Concentration fluctuations and fluxes in plumes from point sources in a turbulent boundary layer. Journal of Fluid Mechanics 117, 1–26] and shows good agreement with the observed mean concentrations and fluctuation intensities. The model is then compared with the wind tunnel simulation of a two-dimensional street canyon by Pavageau, M. and Schatzmann, M. [1999. Wind tunnel measurements of concentration fluctuations in an urban street canyon. Atmospheric Environment 33, 3961–3971]. Despite the limitations of the k–ε turbulence scheme and the IEM mixing mechanism, the model reproduces the fluctuation intensity pattern within the canyon well. Overall, the comparison with both sets of wind tunnel experiments are encouraging, and the simplicity of the model means that predictions in a complex, three-dimensional geometry can be produced in a practicable amount of time.     

Respiratory uptake kinetics of neutral hydrophobic organic chemicals in a marine benthic fish, Pseudopleuronectes yokohamae

We investigated the respiratory uptake kinetics of polychlorinated biphenyls (PCBs), organohalogen pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and 2,2′,4,4′-tetrabrominated diphenyl ether (BDE #47) in a marine benthic fish, Pseudopleuronectes yokohamae. The respiratory uptake efficiencies (E_W) of the chemicals, of which there have been no reports for the majority of persistent organic pollutants (POPs), were obtained by measuring the respiratory uptake rate constants (k₁) and the oxygen consumption rates of fish. Fish were exposed to water in which these chemicals were dissolved at environmentally relevant concentrations for 28 d, followed by 168 d of depuration in clean seawater. The k₁ and E_W values for 99 compounds were obtained, and they ranged from 2000 to 42 000 L kg-lipid⁻¹ d⁻¹ and from 0.060 to 1.3, respectively. The E_W values of the chemicals, except for PAHs, tended to increase with increasing values of the log octanol–water partition coefficients (K_OW) of the chemicals up to a log K_OW of 5. For log K_OW in the range 3–5, the E_W values in this study were much lower than those in a published study (about one-third). As a result of analysis by a two-phase resistance model, the resistance of transport rates to the lipid phase in this study was lower than was the case in the published study. These findings indicate that the E_W predicted by the published study for log K_OW in the range 3–5 may differ among fish species and water temperature, and further study is needed.