Characteristics of puff dispersion in an urban environment |
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| Affiliation: | 1. Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA;2. NOAA Air Resources Laboratory Field Research Division, 1750 Foote Dr., Idaho Falls, ID 83402, USA;1. Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland;2. ETH, Swiss Federal Institute of Technology Zürich, Zürich, Switzerland;3. KIT, Karlsruhe Institute of Technology, Karlsruhe, Germany;4. TU/e, Eindhoven University of Technology, Eindhoven, The Netherlands;1. Department of Neurobiology & Behavior, University of California, Irvine, CA 92697, USA;2. Department of Physiology & Biophysics, University of California, Irvine, CA 92697, USA;1. Mathematics Applications Consortium for Science and Industry (MACSI), Department of Mathematics and Statistics, University of Limerick, Limerick, Ireland;2. Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117576;1. Dept. of Mechanical Engineering, Univ. of Manitoba, Winnipeg, MB R3T 5V6, Canada;2. Defence R&D Canada, Suffield Research Centre, P.O. Box 4000, Stn Main, Medicine Hat, AB T1A 8K6, Canada;1. College of Mathematics and Computation, Hunan Science and Technology University, Xiangtan, Hunan 411201, China;2. Lab of Information Security, Institute of Information Engineering, Chinese Academy of Sciences, Beijing 100093, China |
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| Abstract: | Instantaneous releases of sulfur hexafluoride tracer were carried out as part of the Joint Urban 2003 field campaign in Oklahoma City. Data from 10 fast-response tracer samplers were used to examine the crosswind and along-wind spread of the tracer, the decay of tracer concentrations, and the retention of tracer within approximately 1 km of the release locations. The time variation of the median values of the tracer concentrations, normalized by the peak value observed at a given sampler, could be approximately described by an exponential decay with characteristic decay times on the order of 1–2 min. The longer times were found for early morning releases and the shorter times were associated with later morning or afternoon releases, suggesting that atmospheric stability or the depth of the mixed layer may affect puff dispersion even in urban environments. The median retention times required for 99% of the exposure to be realized at a given location were found to be correlated reasonably well with the median decay times. These characteristic time scales should be regarded as lower limits for concentration decay because the analysis excluded a number of anomalous cases in which the decaying concentrations exhibited an extended tail that indicated a very slow ventilation rate. The median values of the along-wind dispersion parameter σx grouped into downwind distance ranges can be described by a linear variation with distance with an initial “hold up” contribution due to building effects of about 30–45 m, but there are considerable variations about this relationship. Downwind 0.5–1 km from the release point the lateral puff dispersion (σy) was roughly 70% of the along-wind dispersion. |
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