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81.
David R. Worton Claire E. Reeves Stuart A. Penkett William T. Sturges Jana Slemr David E. Oram Brian J. Bandy William J. Bloss Nicola Carslaw James Davey Kathryn M. Emmerson Thomas J. Gravestock Jacqueline F. Hamilton Dwayne E. Heard James R. Hopkins Anne Hulse Trevor Ingram Mark J. Jacob James D. Lee Roland J. Leigh Shona C. Smith 《Atmospheric environment (Oxford, England : 1994)》2010,44(6):773-785
Alkyl nitrates (C1–C5) were measured at two sites (near urban and rural) in southeast England during the Tropospheric Organic Chemistry Experiment (TORCH). Methyl nitrate was the dominant species during both campaigns accounting for on average about one third of the total measured alkyl nitrates. High mixing ratios (>50 pptv) and variability of methyl nitrate were observed at the near urban site (TORCH1) that were not seen at the rural site (TORCH2) and which could not be explained by local photochemical production or direct emissions. The diurnal variation of methyl nitrate during TORCH1 showed a morning maximum that would be consistent with nighttime chemistry followed by transport to the surface by boundary layer dynamics. Similarly, elevated morning mixing ratios were also observed during TORCH2 although the magnitudes were much smaller. As a result, methyl nitrate could represent a tracer for nighttime chemistry seen at the ground the following day. At both campaigns, the dominant source of short chain alkyl nitrates and carbonyl precursor radicals (≤C4) were from decomposition of larger compounds. The magnitude of the source increased with decreasing carbon number consistent with increasing total precursor abundance. Non-photochemical emissions of acetaldehyde and acetone could not be accounted for by automobile exhaust emissions alone and indicated that other direct sources are likely important in this environment. 相似文献
82.
Tatiana Borisova Alan Collins Gerard D’Souza Matthew Benson Mary Leigh Wolfe Brian Benham 《Journal of the American Water Resources Association》2008,44(4):1009-1023
Abstract: Total Maximum Daily Load (TMDL) implementation generates benefits and costs from water quality improvements, which are rarely quantified. This analysis examines a TMDL written to address bacteria and aquatic‐life‐use impairments on Abrams and Opequon Creeks in Virginia. Benefits were estimated using a contingent valuation survey of local residents. Costs were based on the number and type of best management practices (BMPs) necessary to achieve TMDL pollution reduction goals. BMPs were quantified using watershed‐scale water quality simulation models (Generalized Watershed Loading Function and Hydrological Simulation Program‐FORTRAN). Based on our projections, the costs to achieve TMDL induced pollution reduction goals outweigh the estimated benefits. Benefit‐cost ratios ranged between 0.1 and 0.3. 相似文献
83.
Male dung beetles, Onthophagus taurus, are dimorphic for a secondary sexual trait, head horns. Horned males participate in the production of brood masses while
hornless male do not. Here we examine the reproductive performance of females mated with males exhibiting alternative horn
morphologies. We found that exposure to males may be costly for females in that it reduced the total number of brood masses
produced. However, females paired with horned males produced significantly larger brood masses than females paired with hornless
males or females producing broods alone. We discuss the possible selection pressures that may underly horn evolution in this
genus.
Received: 22 August 1997 / Accepted after revision: 19 January 1998 相似文献
84.
Sachs JD Remans R Smukler SM Winowiecki L Andelman SJ Cassman KG Castle D DeFries R Denning G Fanzo J Jackson LE Leemans R Lehmann J Milder JC Naeem S Nziguheba G Palm CA Pingali PL Reganold JP Richter DD Scherr SJ Sircely J Sullivan C Tomich TP Sanchez PA 《Journal of environmental monitoring : JEM》2012,14(3):738-742
The development of effective agricultural monitoring networks is essential to track, anticipate and manage changes in the social, economic and environmental aspects of agriculture. We welcome the perspective of Lindenmayer and Likens (J. Environ. Monit., 2011, 13, 1559) as published in the Journal of Environmental Monitoring on our earlier paper, "Monitoring the World's Agriculture" (Sachs et al., Nature, 2010, 466, 558-560). In this response, we address their three main critiques labeled as 'the passive approach', 'the problem with uniform metrics' and 'the problem with composite metrics'. We expand on specific research questions at the core of the network design, on the distinction between key universal and site-specific metrics to detect change over time and across scales, and on the need for composite metrics in decision-making. We believe that simultaneously measuring indicators of the three pillars of sustainability (environmentally sound, social responsible and economically viable) in an effectively integrated monitoring system will ultimately allow scientists and land managers alike to find solutions to the most pressing problems facing global food security. 相似文献