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Richard A. Brown James G. Mueller Alan G. Seech James K. Henderson John T. Wilson 《补救:环境净化治理成本、技术与工艺杂志》2009,20(1):9-20
While biologically mediated reductive dechlorination continues to be a significant focus of chlorinated solvent remediation, there has been an increased interest in abiotic reductive processes for the remediation of chlorinated solvents. In situ chemical reduction (ISCR) uses zero‐valent iron (ZVI)–based technologies, such as nanoscale iron and bimetallic ZVI, as well as naturally occurring reduced minerals incorporating dual‐valent iron (DVI), such as magnetite, green rust, and iron sulfides that are capable of dechlorinating solvents. A more recent area of development in ISCR has been in combining biological and abiotic processes. There are several ways in which biological and abiotic processes can be combined. First, the interaction between the two may be “causative.” For example, the Air Force Center for Engineering and the Environment's biogeochemical reductive dechlorination (BiRD) technology combines a mulch barrier with hematite and gypsum to create an iron‐sulfide‐based reducing zone. Biodegradation under sulfate‐reducing conditions produces sulfide that combines with the hematite to form iron sulfides. As such, the BiRD technology is “causative”; the biological processes create reducing minerals. The biological generation of other reducing minerals such as magnetite, siderite, and green rust is feasible and is, with magnetite, observed in nature at some petroleum sites. A second type of interaction between abiotic and biotic processes is “synergistic.” For example, biological processes can enhance the activity of reduced metals/minerals. This is the basis of the EHC® ISCR technologies, which combine ZVI with a (slowly) degradable carbon substrate. This combination rapidly creates buffered, strongly reducing conditions, which result in more complete solvent degradation (i.e., direct mineralization). The extent and level of reducing activity commonly observed are much greater when both the carbon substrate and the ZVI are present. When the carbon substrate is expended, the reducing activity due to ZVI alone is much less. The understanding of biogeochemical processes and their impact on abiotic processes is still developing. As that understanding develops, new and improved methods will be created to enhance volatile organic compound destruction. © 2009 Wiley Periodicals, Inc. 相似文献
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Allen S. Lefohn Alan A. Lucier 《Journal of the Air & Waste Management Association (1995)》2013,63(5):694-701
Ambient O3 exposures have reduced growth rates of tree genotypes in some areas of the United States. For characterizing O3 exposures in forested areas, data from primarily population-oriented sites have been used. It has been speculated that exposures calculated from population-oriented sites provide estimates greater than those that would actually be experienced in the majority of forested areas. Accordingly, we compared 1988 O3 data from three remote forested sites with data from several population-oriented monitoring sites in and around the mid? and southern Appalachian Mountains. The number of hours ≥0.08 ppm was lower at the remote forested sites than at the nearby population-oriented locations. In addition, we characterized the temporal variability of O3 exposures in forested regions of the United States and Canada for the period 1978-1988. We found that the years of highest O3 exposure in the eastern United States during 1978-1988 were 1978, 1980, 1983, and 1988, with 1988 being the worst year in four of seven eastern forest regions. In 1988, the Whiteface Mountain summit site (1483 m) experienced approximately 10 percent more hourly average concentrations ≥0.08 ppm than in the second highest O3 exposure year (i.e., 1979). Consistently throughout the 11-year period, the highest O3 exposures at the Whiteface Mountain site occurred during the late evening and early morning hours, with the result that the longterm 7-h (0900-1559h) exposure index could not distinguish those years in which the highest exposures occurred from those in which the lowest occurred. Similar to the Whiteface Mountain site, two high-elevation Shenandoah National Park sites experienced their highest O3 exposures in 1988. With the exception of 1986, the lower elevation site (Dickey Ridge) consistently experienced more frequent occurrences of hourly average concentrations ≥0.08 ppm than the higher elevation site (Big Meadows). 相似文献
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William R. Pierson Alan W. Gertler Ronald L. Bradow 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1495-1504
The Van Nuys Tunnel experiment conducted in 1987 by Ingalls et al. (see A&WMA Paper 89-137.3), to verify automotive emission inventories as part of the Southern California Air Quality Study (SCAQS), gave higher CO and HC emission-rate values than expected on the basis of automotive-emission models—by factors of approximately 3 and 4, respectively. The CO/NOX and HC/NOX emission-rate ratios moreover were higher than expected—by similar factors (NOX emission rates were about as expected). The purpose of the present paper is to review the literature on dynamometer and on-road (in tunnels and along roadways) testing of in-use vehicles, and on urban-air CO/HC/NOX concentration ratios, to see whether the Van Nuys Tunnel results are reasonable in terms of previous experience. The conclusions are that (1) on-road CO and HC emissions higher than expected have been reported before, (2) on-road CO and HC emissions consistent with the Van Nuys Tunnel results have been reported before, and (3) on-road CO/NOX and HC/NOX emission-rate ratios higher than expected have been reported before. The Van Nuys Tunnel NOX results actually are lower than in other on-road experiments, and the CO/NOX and HC/NOX ratios consequently are higher. The higher-than-predicted CO/NOX and HC/NOX ratios at Van Nuys and other on-road sites suggest richer operation on-road than predicted or than observed in the inuse- vehicle dynamometer tests which serve as the model inputs. Support for these suggestions and conclusions is found in comparison of urban-air and emission-inventory HC/NOX ratios. 相似文献
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Watson A Glaspell B Christensen N Lachapelle P Sahanatien V Gertsch F 《Environmental management》2007,40(6):880-888
Many public land management agencies are committed to understanding and protecting recreation visitor experiences. Parks Canada
is deeply committed to that objective for visitors to Canada’s National Parks. This 2004 study, informed by a 2003 qualitative
study of visitor experiences and influences on those experiences at Auyuittuq National Park in Nunavut, worked to bring 50
potential elements of visitor experiences down to five articulated dimensions of the experience that is currently being received
at this remote eastern arctic park. A hypothesized set of 17 influences on experiences, also reduced to just two factors with
similar response patterns, and with some items that did not flow into the two factors, were used in a regression analysis
to understand the relationship between experiences and factors of influence. A sample of 61.8% (84) of the total recreation
visitor population 16 years of age or older was surveyed during deregistration after the trip. Knowledge about the dimensions
of the experiences currently received and factors of influence on those experiences can be used to guide selection of indicators
for describing objectives and prescribing monitoring protocol. 相似文献