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排序方式: 共有182条查询结果,搜索用时 265 毫秒
131.
Nick Jordan Natasha M. Garner Laura C. Matchett Travis W. Tokarek Charles A. Odame-Ankrah 《Journal of the Air & Waste Management Association (1995)》2020,70(8):753-764
ABSTRACT Mixing ratios of the criteria air contaminant nitrogen dioxide (NO2) are commonly quantified by reduction to nitric oxide (NO) using a photolytic converter followed by NO-O3 chemiluminescence (CL). In this work, the performance of a photolytic NO2 converter prototype originally designed for continuous emission monitoring and emitting light at 395 nm was evaluated. Mixing ratios of NO2 and NOx (= NO + NO2) entering and exiting the converter were monitored by blue diode laser cavity ring-down spectroscopy (CRDS). The NO2 photolysis frequency was determined by measuring the rate of conversion to NO as a function of converter residence time and found to be 4.2 s?1. A maximum 96% conversion of NO2 to NO over a large dynamic range was achieved at a residence time of (1.5 ± 0.3) s, independent of relative humidity. Interferences from odd nitrogen (NOy) species such as peroxyacyl nitrates (PAN; RC(O)O2NO2), alkyl nitrates (AN; RONO2), nitrous acid (HONO), and nitric acid (HNO3) were evaluated by operating the prototype converter outside its optimum operating range (i.e., at higher pressure and longer residence time) for easier quantification of interferences. Four mechanisms that generate artifacts and interferences were identified as follows: direct photolysis, foremost of HONO at a rate constant of 6% that of NO2; thermal decomposition, primarily of PAN; surface promoted photochemistry; and secondary chemistry in the connecting tubing. These interferences are likely present to a certain degree in all photolytic converters currently in use but are rarely evaluated or reported. Recommendations for improved performance of photolytic converters include operating at lower cell pressure and higher flow rates, thermal management that ideally results in a match of photolysis cell temperature with ambient conditions, and minimization of connecting tubing length. When properly implemented, these interferences can be made negligibly small when measuring NO2 in ambient air. Implications: A new near-UV photolytic converter for measurement of the criteria pollutant nitrogen dioxide (NO2) in ambient air by CL was characterized. Four mechanisms that generate interferences were identified and investigated experimentally: direct photolysis of HONO which occurred at a rate constant 6% that of NO2, thermal decomposition of PAN and N2O5, surface promoted chemistry involving HNO3, and secondary chemistry involving NO in the tubing connecting the converter and CL analyzer. These interferences are predicted to occur in all NO2 P-CL systems but can be avoided by appropriate thermal management and operating at high flow rates. 相似文献
132.
Ryan Shepler Jordan F. Suter Dale T. Manning Chris Goemans 《Journal of the American Water Resources Association》2019,55(3):657-669
Conservation of groundwater resources is critical for maintaining the future productivity of irrigated land in the Ogallala Aquifer Region and beyond. This research explores motivations and behavior related to groundwater conservation among agricultural producers in the Colorado portion of the Republican River Basin, which is part of the Ogallala Aquifer. The empirical modeling uses data from a recently conducted survey to analyze how a common set of producer, farm, and resource characteristics influence groundwater values, concern for future groundwater availability, private conservation actions, and support for coordinated conservation efforts. We find two factors, producer age and land owner status, are consistently correlated with the key conservation‐related outcomes we evaluate. More generally, the results suggest considerable similarities in the characteristics that drive private conservation actions and support for coordinated conservation. This knowledge could be used to better target and incentivize future groundwater conservation efforts in the region. Editor's note : This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series. 相似文献
133.
ABSTRACTThe European Union (EU) has had a profound effect upon its members’ environmental policy. Even in the United Kingdom (UK), the EU’s most recalcitrant member state (historically labeled the ‘Dirty man of Europe’), environmental policy has been Europeanised. As the UK moves to the EU’s exit door it is timely to assess the utility of Europeanisation for understanding policy dynamics in the UK. Drawing upon interviews and extensive engagement with stakeholders, this article analyses the potential impact of Brexit upon environmental policy and politics. The analytical toolkit offered by de-Europeanisation is developed to identify the factors that drive and inhibit de-Europeanisation processes, thereby providing insights that may be applicable in other settings. Disengagement and policy stagnation are presented as more likely environmental outcomes of Brexit, with capacity emerging as a central explanatory variable. 相似文献
134.
135.
R. B. Rosengaus C. Jordan M. L. Lefebvre J. F. A. Traniello 《Die Naturwissenschaften》1999,86(11):544-548
Dampwood termites, Zootermopsis angusticollis, show an alarm response after detecting the presence of spores of the pathogenic fungus Metarhizium anisopliae. Termites in direct contact with a high concentration of spores (107 spores/ml) show a striking vibratory display which appears to convey information about the presence of pathogens to nearby
unexposed nestmates through substrate vibration. Nestmates not directly in contact with spores that perceive the vibrational
signal increase significantly their distance from the spore-exposed vibrating termites, apparently to escape from the source
of infection. The fleeing response is not induced by the presence of the spores alone or by pheromones, and requires the perception
of the vibrations propagated through the substrate. This "pathogen alarm behavior" appears to be a previously unrecognized
communication mechanism that allows termites to reduce disease risks within the nest.
Received: 12 May 1999 / Accepted in revised form: 26 August 1999 相似文献
136.
A decision inventory approach for improving decision support for climate change impact assessment and adaptation 总被引:1,自引:0,他引:1
Christopher R. Britta G. John Janet Thomas Susan Jordan 《Environmental Science & Policy》2007,10(7-8):610-621
Assessing and adapting to the impacts of climate change requires balancing social, economic, and environmental factors in the context of an ever-expanding range of objectives, uncertainties, and management options. The term decision support describes a diverse class of resources designed to help manage this complexity and assist decision makers in understanding impacts and evaluating management options. Most climate-related decision support resources implicitly assume that decision making is primarily limited by the quantity and quality of available information. However, a wide variety of evidence suggests that institutional, political, and communication processes are also integral to organizational decision making. Decision support resources designed to address these processes are underrepresented in existing tools. These persistent biases in the design and delivery of decision support may undermine efforts to move decision support from research to practice. The development of new approaches to decision support that consider a wider range of relevant issues is limited by the lack of information about the characteristics, context, and alternatives associated with climate-related decisions. We propose a new approach called a decision assessment and decision inventory that will provide systematic information describing the relevant attributes of climate-related decisions. This information can be used to improve the design of decision support resources, as well as to prioritize research and development investments. Application of this approach will help provide more effective decision support based on a balanced foundation of analytical tools, environmental data, and relevant information about decisions and decision makers. 相似文献
137.
138.
A comparison of the quantification of a specific microbial group in activated sludge by fluorescent in-situ hybridization, coupled with either direct microscopic counting or flow cytometry, was performed using an enhanced-biological-phosphorus-removal, sequencing-batch reactor. The population dynamics of Candidatus Accumulibacter phosphatis (Cand. A. phosphatis) was evaluated during two separate runs of the reactor. With the operational conditions used, Cand. A. phosphatis was enriched until a failure in the pH controller eliminated its ecological advantage. As a result, the comparison of quantification techniques included Cand. A. phosphatis concentrations as low as 11% and as high as 96% of the total cells in the samples. The analysis demonstrated that, regardless of the particular limitations of each technique, both provided similar results when the activated-sludge flocs were easily dispersed. However, when the activated-sludge samples contained flocs that were difficult to disperse, flow cytometry failed to provide quantitative results. 相似文献
139.
140.
Pengcheng Xun Kiang Liu J. Steve Morris Joanne M. Jordan Ka He 《Environmental science and pollution research international》2013,20(3):1423-1430
Since data on mercury (Hg) levels in Caucasians and African Americans (AAs) of both genders are lacking, this study aims to present toenail Hg distributions and explore the potential determinants using data from the Coronary Artery Risk Development in Young Adults Trace Element Study. Data from 4,344 Americans, aged 20–32 in 1987, recruited from Oakland, Chicago, Minneapolis, and Birmingham were used to measure toenail Hg levels by instrumental neutron-activation method. The Hg distribution was described with selected percentiles and geometric means. Multivariable linear regression (MLR) was used to examine potential determinants of Hg levels within ethnicity–gender subgroups. The geometric mean of toenail Hg was 0.212 (95 % CI?=?0.207–0.218)?μg/g. Hg levels varied geographically with Oakland the highest [0.381 (0.367–0.395) μg/g] and Minneapolis the lowest [0.140 (0.134–0.147) μg/g]. MLR analyses showed that male gender and AA ethnicity were negatively associated with toenail Hg levels, and that age, living in Oakland city, education level, alcohol consumption, and total fish intake were positively associated with toenail Hg concentrations within each ethnicity–gender subgroup. Current smokers were found to have higher Hg only in AA men. This study suggested age, gender, ethnicity, study center, alcohol, education level, and fish consumption consistently predict toenail Hg levels. As fish consumption was the key determinant, avoiding certain types of fish that have relatively high Hg levels may be crucial in reducing Hg intake. 相似文献