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91.
Kelly P. Grogan Robert A. Fjeld Timothy A. DeVol 《Journal of environmental radioactivity》2010,101(10):847-853
The effect of the spatial variability of Kd on calculations of contaminant travel time in the vadose zone was determined. Depth discrete measurements of Kd were made for a suite of radionuclides (109Cd, 57Co, 60Co, 85Sr, 137Cs, and 88Y) utilizing a sediment core from the E-Area at the Savannah River Site. The Kd’s were ordered as 85Sr2+ < 137Cs+ < 109Cd2+ < 57Co2+ = 60Co2+ << 88Y3+ and the values generally fell below or near the lowest quartile of values reported in the literature. Correlations were generally weak between soil properties and Kd values. Most importantly, all of the Kd distributions could be reasonably approximated as log-normal. Deterministic and stochastic calculations of contaminant travel time to the water table were made. The deterministic calculations were based on each of three conceptual models of the vadose zone: complete stratification (17 strata, each with a different Kd), two strata (two sections of the vadose zone, each characterized by a single, average Kd), and unstratified (a single zone with an average Kd). Stochastic calculations were based on log-normal fits to the Kd data. The two strata model generally yielded travel times 2× greater than those in the completely stratified model. The unstratified model yielded travel times that were between 3 and 5 times greater than the completely stratified model. The stochastic mean travel times were comparable to those of the two strata model. 相似文献
92.
Y. Valcárcel S. González Alonso J. L. Rodríguez-Gil A. Castaño J. C. Montero J. J. Criado-Alvarez I. J. Mirón M. Catalá 《Environmental science and pollution research international》2013,20(3):1396-1412
Numerous studies have shown the presence of pharmaceutically active compounds (PhACs) in different environmental compartments, for example, in surface water or wastewater ranging from nanograms per litre to micrograms per litre. Likewise, some recent studies have pointed to seasonal variability, thus indicating that PhAcs concentrations in the aquatic environment may depend on the time of year. This work intended to find out (1) whether Tagus fluvial and drinking water were polluted with different groups of PhACs and (2) if their concentrations differed between winter and summer seasons. From the 58 substances analysed, 41 were found belonging to the main therapeutic groups. Statistical differences were seen for antibacterials, antidepressants, anxiolytics, antiepileptics, and cardiovascular drugs, with higher concentrations being detected in winter than in summer. These results might indicate that the PhACs analysed in this study undergo lower environmental degradation in winter than in summer. In order to confirm these initial results, a continuous monitoring should be performed especially on those PhACs that either because of an elevated consumption or an intrinsic chemical persistence are poorly degraded during winter months due to low temperatures and solar irradiation. It is especially important to identify which of these specific PhACs are in order to recommend their substitution by equally effective and safe substances but also environmentally friendly. 相似文献
93.
Andy L. Sandy Jia Guo Robert J. Miskewitz Wade R. McGillis Lisa A. Rodenburg 《Chemosphere》2013,90(5):1637-1643
Air–water exchange is an important process controlling the fate of many organic chemicals in the environment. Modeling this process is hampered by the lack of direct observations. Thus, the purpose of this work was to derive direct measurements of the mass transfer coefficients for air–water exchange (vaw) of polychlorinated biphenyls (PCBs) that may be used to check the validity of values derived from tracer gas experiments. vaw values for PCBs were determined using previously published turbulent fluxes divided by the corresponding dissolved phase concentrations. The median vaw values for each homolog decreased with increasing molecular weight and ranged from 0.29 for hexachlorobiphenyls to 2.2 m d?1 for monochlorobiphenyls with a propagated uncertainty of about 70%, lower than in previous studies. Due to relatively low wind speeds and possible sorption of PCBs to colloids, these numbers may be biased low. These field measurements of vaw differ by as much as a factor of 23 from predictions based on the widely-used Whitman two-film model. Therefore a new formulation for the calculation of vaw based on field measurements is needed. This study demonstrates that micrometeorological approaches are a viable option for the measurement of vaw for hydrophobic organics such as PCBs and should be used to generate enough field data on the air–water exchange of hydrophobic organics to allow the development of new predictive models. 相似文献
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Robert E. Kunkle 《Journal of the Air & Waste Management Association (1995)》2013,63(6):274-277
The feasibility of open burning under selected meteorological conditions is discussed. Meteorological provisos and nonmeteorological factors are enumerated. Topics discussed include: combustion, fuel moisture, fire hazard, forecasting, fallout and odor, and air pollution potential. A mathematical estimate of visibility reduction is described and evaluated. A procedure for estimating atmospheric ventilation is presented. The author concludes that most massive open fires result in adverse effects on either a local or areawide scale. Hence, the best meteorological decision possible is frequently one that minimizes one scale of effect at the expense of the other. 相似文献
96.
The photochemical reaction of various olefins and nitrogen dioxide was studied under conditions of controlled temperature, pressure, and humidity in a 200 liter stirred glass reactor. The hydrocarbon concentration in the reactor during four and five hour irradiation periods was monitored with a flame ionization chromatograph. Reaction rate constants, based on three consecutive first order reactions, were calculated for reactor temperatures of 20, 25, 30, and 35 degrees centigrade. Activation energies for the three consecutive reactions were calculated from the Arrhenius equation. Branched and straight chain olefins were studied at initial concentrations of 5.0 to 10.0 parts per million.s 相似文献
97.
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100.
Robert A. O'Dell Mansoor Taheri Robert L. Kabel 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1104-1109
A mass transfer approach is used in developing a practical mathematical model of gaseous pollutant uptake by leaves in which a series of resistances is summed across a concentration difference. The body of information presented in this paper is directed to plant pathologists or physiologists in the field of vegetal-pollutant effects and to people interested in the natural removal of air pollutants by vegetation. Correlations are given to calculate the aerodynamic and the stomatal resistances to uptake, while both a qualitative investigation and quantitative estimates are made of the mesophyllic resistance. The factors which control the aerodynamic resistance, ra, are leaf size and wind speed, while the leaf physiology is the determinant of the stomatal resistance, rs . It is noted that the chemical reaction rate and pollutant diffusivity in the mesophyll control the mesophyllic resistance, rm, though the overall gas phase mesophyllic resistance, Hrm, is strongly a function of pollutant solubility in water. Finally, the overall model is compared to earlier experimental work on vegetal uptake of SO2. 相似文献