A physicochemical model of the fate of toxic substances in the Great Lakes was constructed from mass balance principles, incorporating principal mechanisms of particulate sorption-desorption, sediment-water and atmosp...
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A physicochemical model of the fate of toxic substances in the Great Lakes was constructed from mass balance principles, incorporating principal mechanisms of particulate sorption-desorption, sediment-water and atmosphere-water interactions, and chemical and biochemical decay. The steady state mass balance model of the suspended solids in the open lake water yielded net solids loss rates from 0.02 m/day for Saginaw Bay to 1.22 m/day or Lake Ontario. Calibration of the toxic model was through comparison to 239Pu data collected in the 1970s using a 23 yr time variable calculation. In general, the sediments were interactive with the water column in the Great Lakes through resuspension and horizontal transport. Response times (50%) of 239Pu following a cessation of load extend beyond 10 yr with sediment resuspension. The calibrated model was also applied to polychlorinated biphenyl (PCB) using a high and low estimate of contemporary external load and with and without volatilization. The lower load level (lake range 640-1390 kg/yr) with volatilization (at an exchange rate of 0.1 m/day) was more representative of observed surface sediment data for the open lake waters. Calculated water column concentrations for the lower load level with and without volatilization ranged from 0.25-0.90 ng/l for open lake waters. Response times (50%) for PCB following cessation of load varied from < 5 yr when volatilization was included to 10-20 yr without volatilization. Comparison of these response times to decline of concentrations of PCB in Lake Michigan bloaters indicated that, at least for that lake, volatilization occurred at an exchange rate of .apprx. 0.1 m/day.
The extent of reversibility of PCB [polychlorinated biphenyl] bonding to sediments was characterized in studies on the partitioning behavior of hexachlorobiphenyl isomer. Linear nonsingular isotherms were observed for...
The extent of reversibility of PCB [polychlorinated biphenyl] bonding to sediments was characterized in studies on the partitioning behavior of hexachlorobiphenyl isomer. Linear nonsingular isotherms were observed for the adsorption and desorption of 2,4,5,2'',4,'',5''-hexachlorobiphenyl (HCBP) to 1100 ppm sediment suspensions. Partition coefficients, (.pi.l/kg), for desorption from lake sediments (Saginaw Bay, Lake Huron, Michigan) [USA] were substantially greater (.pi.d .apprx. 20,000-35,000) than those obtained for adsorption (.pi.a .apprx. 9000-14,000). HCBP was more weakly adsorbed to montmorillonite (.pi.a .apprx. 3000, .pi.d .apprx. 9000) and kaolinite (.pi.a .apprx. 1000, .pi.d .apprx. 3000) clay samples than to the natural sediment samples. Desorption results (.pi.d) for Saginaw Bay sediments were similar to .pi. values (15,000-35,000) calculated from field measurements of aqueous and particulate PCB concentrations. For Saginaw Bay sediments and clay minerals partitioning was correlated to sediment surface area and sediment organic content. A regression analysis using both variables explained .apprx. 90% of the observed variations. HCBP adsorption at ***. C (.pi.a .apprx. 14,000) was significantly greater than at ***. C (.pi.a .apprx. 6500) resulting in a calculated enthalpy of adsorption of +3.3 kcal/mol. Nonsingular isotherm behavior was not readily attributable to microbiological, kinetic or experimental effects. Evidence from consecutive desorption studies suggested that while HCBP adsorption may have been ultimately reversible, release from sediments probably involved desorption along 2 distinct isotherms. These results were interpreted in terms of possible similarities between the sorption properties observed in distilled water systems and PCB bonding processes in natural water systems.
Gaseous NH 3 and HNO 3 were continuously and rapidly removed from an aerosol containing small, aqueous solution droplets of NH 4 NO 3 (MMD = 0.4 μm), resulting in evaporation of the NH 4 NO 3 from the droplets. The r...
Gaseous NH 3 and HNO 3 were continuously and rapidly removed from an aerosol containing small, aqueous solution droplets of NH 4 NO 3 (MMD = 0.4 μm), resulting in evaporation of the NH 4 NO 3 from the droplets. The rate of evaporation was measured by following changes in the size distribution of the aerosol with time. The measured rates agree well with those predicted from existing theories of gaseous diffusion and concentrated solution chemistry. The resulting ‘evaporation’ coefficient for both NH 3 and HNO 3 was unity, implying that resistance to transport of molecules across the vapor-liquid interface is small. The observed rates imply negligible sampling errors from evaporation of NH 4 NO 3 in gas denuder tubes used in atmospheric measurements of HNO 3 and particulate nitrate compounds.
We report measurements taken in Houston, Texas of the chemical composition and degree of hydration of haze particles and compare these results with previously reported measurements taken in rural Virginia. Our in-situ...
We report measurements taken in Houston, Texas of the chemical composition and degree of hydration of haze particles and compare these results with previously reported measurements taken in rural Virginia. Our in-situ, real time measurements are based on detecting changes in particle light scattering extinction with changes in relative humidity and air temperature. With these methods we can determine fine particle mass and sulfate mass concentrations, and sulfate to ammonium ion molar ratio. In Houston, fine particle sulfate averaged 42 % of fine particle mass and the composition in terms of ammonium to sulfate molar ratio ranged from 0.5 to 2 with strong diurnal variation. The particles were most acid during the period 1500 to 2000 and neutral during 0200 to 0900. About 1 3 of the time the particles were droplets supersaturated in terms of salt content. In Virginia, the particles were on average more acidic and contained more water than those in Houston, but the particles were never observed to be supersaturated solution droplets. The difference in the hygroscopic behavior of the particles at the two sites is consistent with differences in both particle chemistry and ambient relative humidity.
The potential use of rudders as anti-roll devices has long been recognized. However, the possible interference of this secondary function of the rudder with its primary role as the steering mechanism has prevented, fo...
The potential use of rudders as anti-roll devices has long been recognized. However, the possible interference of this secondary function of the rudder with its primary role as the steering mechanism has prevented, for many years, the development of practical rudder roll stabilizers. The practical feasibility of rudder roll stabilization has, however, in recent years been demonstrated by two systems designed and developed for operational evaluation aboard two different U.S. C oast G uard Cutters, i.e., Jarvis and Mellon of the 3,000-ton, 378-foot HAMILTON Class. The authors describe the major components of the rudder roll stabilization (RRS) system, along with the design goals and methodology as applied to these first two prototypes. In addition, a brief history of the hardware development is provided in order to show some of the lessons learned. The near flawless performance of the prototypes over the past four years of operational use in the North Pacific is documented. Results from various sea trials and reports of the ship operators are cited and discussed. The paper concludes with a discussion of the costs and benefits of roll stabilization achieved using both a modern anti-roll fin system, as well as two different performance level RRS systems. The benefits of roll stabilization are demonstrated by the relative expansion in the operational envelopes of the USS OLIVER HAZARD PERRY (FFG-7) Class. The varying levels of roll stabilization suggest that the merits of fins and RRS systems are strongly dependent on mission requirements and the environment. The demonstrated performance of the reliable RRS system offers the naval ship acquisition manager a good economical stabilization system.
A new technique has been developed for determination of optical depths δ a as low as 0.0005 for thin layers of absorbing materials or particles. The measurement involves optical amplification of the absorption and is...
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A new technique has been developed for determination of optical depths δ a as low as 0.0005 for thin layers of absorbing materials or particles. The measurement involves optical amplification of the absorption and is not affected by the scattering properties of the absorber. This is accomplished by introducing the absorber into the virtually isotropic radiation field between two high-reflectance diffusing wafers and measuring the resultant attenuation of the transmitted light. The technique has been directed toward determination of the absorption coefficient of atmospheric aerosols in remote and relatively unpolluted locations. Provided appropriate collection filters and sampling conditions are used, the method can establish an absorption coefficient for the aerosol as low as 5 × 10 −9 m −1 within a 10-h sampling period. A proportionally higher absorption coefficient requires proportionally less sample time. This paper discusses instrument design, the theoretical optical model, laboratory calibration, and a field test of the technique.
Optical properties of Nuclepore filter media, as used in the integrating plate (IP) method for determination of aerosol light absorption, have been examined. It has been shown that the internal reflectance is high for...
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Optical properties of Nuclepore filter media, as used in the integrating plate (IP) method for determination of aerosol light absorption, have been examined. It has been shown that the internal reflectance is high for the Nuclepore filters typically used and that changes in this value result in spurious contributions to absorption measurements. It has been found that aerosol particles on the filter surface can substantially alter the internal reflection coefficient of this material for a wide variety of aerosol types. The amount and nature of this change are found to vary with optical and physical properties of the aerosol in contact with the filter surface. A simple mathematical model of the optical system is described that allows for variations in Nuclepore internal reflectance. Implications of this model and data suggest that light absorption measurements as determined via the IP method may be systematically overestimated for certain samples by as much as 30%. Estimates of the magnitude of this inaccuracy for a given IP absorption measurement are presented based on the model and supplementary back reflectance measurements.
Results from laboratory equilibration studies indicate that sediment-adsorbed 2,4,5,2′,4′,5′-hexachlorobiphenyl (HCBP) fractions may be comprised of both reversibly and strongly bound or resistant components. This ...
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