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711.
712.
713.
Charles M. Buchanan Barry G. Pearcy Alan W. White Matthew D. Wood 《Journal of Polymers and the Environment》1997,5(4):209-223
The miscibility of cellulose acetate (CA; degree of substitution = 2.5) and poly(ethylene succinate) (PES) has been investigated
using a variety of thermal techniques and by solid-state carbon13 NMR spectroscopy. The blends containing greater than ca.
70% CA were found to be miscible. In the case of blends containing less than ca. 70% CA, a combination of thermal and NMR
analyses suggests that these blends are not fully miscible on a 2.5- to 5-nm scale. On the scale which can be probed by dynamic
mechanical thermal analysis (15 nm), the low-percentage CA blends exhibit “significant local concentration fluctuations≓.
Investigation of the biodegradation of the blend components and of the blends revealed that PES degraded relatively rapidly
and that CA degraded slowly. The blends degraded at a rate essentially identical to that of CA. Miscibility (75% CA blend)
or crystallization of PES (30% CA blend) had no significant effect. These data suggest that a significant mode of degradation
ófPES during composting involves chemical hydrolysis of the polymer followed by biological assimilation of monomers. Degradation
of the blends is initiated in the amorphous phase. Because CA is a significant component of the amorphous phase, a small amount
of CA significantly impacts the biodegradation rates of the blends. 相似文献
714.
Todd A. Anderson Devin M. Scherubel Rong Tsao Alan W. Schwabacher Joel R. Coats 《Journal of Polymers and the Environment》1997,5(2):119-124
Determining the fate of xenobiotic materials in the environment can be aided by the use of radioactive isotope technology.
Previous research on the degradation of polymers such as polyethylene (PE) was aided by the utilization of radiotracers. In
order to study the environmental fate of degradable (PE/starch) plastics, we synthesized3H-labeled PE. Results of soil incubation studies indicate that only minimal degradation of the PE component, as indicated
by the production of water-soluble metabolites, occurred during 2 years of incubation in soil. Despite the minimal degradation,
the3H label did not allow for detection of the degradation products. In addition, the3H-PE was particularly useful for tracing the fate of degradable plastics after consumption by terrestrial isopods. The detection
of aqueous-soluble radioactivity in isopod frass was used to indicate degradation of the plastic film. 相似文献
715.
Abu-Allaban M Rogers CF Gertler AW 《Journal of the Air & Waste Management Association (1995)》2004,54(3):360-366
During the period May 18-May 22, 1999, a comprehensive study was conducted in the Tuscarora Mountain Tunnel on the Pennsylvania Turnpike to measure real-world motor-vehicle emissions. As part of this study, size distributions of particle emissions were determined using a scanning mobility particle sizer. Each measured size distribution consisted of two modes: a nucleation mode with midpoint diameter less than 20 nm and an accumulation mode with midpoint diameter less than 100 nm. The nucleation and accumulation components in some distributions also exhibited second maxima, which implies that such particle size distributions are superpositions of two particle size distributions. This hypothesis was utilized in fitting the particle size distributions that exhibited second maxima with four lognormal distributions, two for the nucleation mode and two for the accumulation mode. The fitting assumed that the observed particle size distribution was a combination of two bimodal log-normal distributions, one attributed to the heavy-duty diesel (HDD) vehicles and another attributed either to a different class of HDD vehicles or to the light-duty spark ignition vehicles. Based on this method, estimated particle production rates were 1.8 x 10(13) and 2.8 x 10(14) particles/vehicle-km for light-duty spark ignition and HDD vehicles, respectively, which agreed with independently obtained estimates. 相似文献
716.
Alan M. Jones Roy M. Harrison 《Atmospheric environment (Oxford, England : 1994)》2006,40(40):7733-7741
Proposals from the European Commission have raised the possibility that Member States may be able to subtract the concentrations of natural components of airborne particulate matter from measured concentrations when evaluating compliance with EU Limit Values. By applying the pragmatic mass closure model [Harrison et al., 2003. A pragmatic mass closure model for airborne particulate matter at urban background and roadside sites. Atmospheric Environment 37, 4927–4933] to chemical composition data for PM10, it has been possible to estimate the concentrations of natural sea salt, strongly bound water and secondary organic carbon (which is assumed wholly biogenic) to the measured mass of PM10. Because of the difficulty in distinguishing between natural and anthropogenic crustal dusts, the contribution of natural windblown dust and soil has not been accounted for. When the natural components are estimated for two urban and one rural site in the UK, the long-term mean PM10 concentration is reduced by between 5.2 and 7.3 μg m−3. The number of exceedences of the 50 μg m−3 24-h limit value falls dramatically from 54 to 21 (from a total of 291 days) at an urban street canyon site, 7 to 3 (n=292 days) at an urban background site and from 8 to 0 (n=241 days) at a rural site when using gravimetric PM10 concentrations. The calculations have also been performed using PM10 concentrations measured by TEOM increased by a factor of 1.3 as recommended by the European Commission as an interim means of estimating gravimetric equivalency, and the number of exceedences of the 24-h limit value fell from 92 to 47 (from a total of 291 days) at the urban street canyon site, from 11 to 3 (n=292 days) at the urban background site and from 6 to 3 (n=241) at the rural site. Clearly, therefore, application of this proposed measure would make a very major difference to the likelihood of compliance or otherwise with the 24-h limit value for PM10. 相似文献
717.
Ramakrishnan B Sorial GA Speth TF Clark P Zaffiro A Patterson C Hand DW 《Journal of the Air & Waste Management Association (1995)》2004,54(5):529-539
The widespread use of methyl tertiary butyl ether (MTBE) as an oxygenate in gasoline has resulted in the contamination of a large number of ground and surface water sources. Even though air stripping has been proven to be an effective treatment technology for MTBE removal, off-gas treatment often is required in conjunction with it. This study evaluated the combined treatment technologies of air stripping followed by off-gas adsorption on a pilot scale for the treatment of MTBE-contaminated water. The effect of air/water ratios on the treatment efficiency was studied, and the mass transfer coefficient was determined. Air/water ratios of 105:1, 151:1, 177:1, 190:1, 202:1, and 206:1 were used, and a treatment efficiency of >99% was achieved for all the runs conducted. The depth of packing required to achieve maximum treatment efficiency decreased with increasing air/water ratio. Relative humidity (RH) impacts on the MTBE adsorption capacity of a granular activated carbon (GAC) and carbonaceous resin were determined from pilot plant studies. Breakthrough profiles obtained from the pilot plant studies conducted at 20, 30, and 50% RH indicated that GAC has a higher adsorptive capacity than resin. The adsorptive capacity of GAC decreased with increasing RH, whereas RH did not impact the resin adsorptive capacity. 相似文献
718.
A series of workshops have provided extensive feedback on a recently published manual, Monitoring Guidelines to Evaluate Effects of Forestry Activities on Streams in the Pacific Northwest and Alaska (Guidelines) (MacDonald et al., 1991). These workshops and other discussions have led to the identification of fourteen additional lessons for monitoring. These lessons are concepts which either were not incorporated into the Guidelines, were not sufficiently emphasized, or which are needed to put the Guidelines in context. The topics include: monitoring as a continuum; defining objectives and hypotheses; peer review; uncertainty and risk; upslope vs. instream monitoring; photo sequences; scale considerations; data storage, data interpretation, and data base management; activities monitoring; and personal commitment as a critical component in monitoring projects. Many of these lessons might appear self-evident, but our experience indicates that they are often ignored. Like the Guidelines, these lessons are widely applicable and should be explicitly recognized when formulating and conducting monitoring projects. 相似文献
719.
Winter Quarters Bay (WQB) is a small embayment located adjacent to McMurdo Station, the largest researchbase in Antarctica. The bay is approximately 250 m wide andlong, with a maximum depth of 33 m. Historically, trashfrom the McMurdo Station was piled on the steep shoreline ofWQB, doused with fuel and ignited. That practice hasceased, and the adjacent land area has been regraded tocover the residual waste. The bottom of WQB remainslittered with drums, equipment, tanks, tires, cables, andother objects, especially the southeastern side of the baywhere dumping took place. Sediments are contaminated withPCBs, metals, and hydrocarbon fuels. The objectives of this study were to map the distributionof organic contaminants in WQB, assess the toxicity of WQB sediments using a simple microbial test, anddetermine correlations between toxicity and contaminantlevels. The study suggests that adverse ecological effectshave occurred from one or more of the contaminants found inWQB but the source of the toxic impacts to bay sedimentsremains unknown. Whole sediment toxicity was onlycorrelated with oil-equivalent while solvent extracts ofsediments were correlated with PAHs and oil-equivalent. Theauthors recommend that an integrated research plan bedeveloped that focuses on determining what additionalinformation is needed to make informed decisions on possibleremediation of WQB. 相似文献
720.
May PH Dabbs AW Fernández-Dávila P Da Vinha V Zaidenweber N 《Environmental monitoring and assessment》2002,76(1):125-134
The prevailing corporate trend regardingdevelopment of energy resources in the tropics emphasizesfinancial gain over long-term societal benefits. Somecorporations are beginning to find a competitive advantage linkedto proactive relations with host communities and adequateprotection of fragile ecosystems. Herein, we describe a casestudy where an international energy production company workedwith stakeholders to achieve social capital and sustainabledevelopment. The strategies aimed to strengthen local capacity toimprove social welfare and to ensure conservation and wise use ofbiodiversity. We provide examples, discuss lessons learned andmake recommendations for future development projects. 相似文献