examination of the pasquill gifford turner dispersion 的帕斯奎尔吉福特纳分散检查课件

Performance of Air Quality Models in Urban Areas Objectives and Motivation St. Louis study and ISC urban Model Improvements Performance of Improved Model Conclusions Akula Venkatram1, Vlad Isakov2, 1University of California, Riverside, CA 2NOAA, NERL, RTP, NC Motivation and Objectives The most severe air pollution problems in Asia are caused by emissions in urban areas uExamine the performance of currently used urban air quality models-ISC uSuggest improvements based on recent tracer studies in urban areas St. Louis Experiment Conducted during 1963-1965 resulting in 26 daytime and 16 nighttime experiments Cadmium sulfide particles released from ground- level source and measured at distances ranging from 800 m to 16 km using 50 samplers Winds, temperature, and horizontal velocity fluctuations measured using TV tower and tether sondes upto a height of 140 m. Briggs (1974) used data to derive McElroy- Pooler urban dispersion curves used in ISC McElroy-Pooler Curves Briggs(1974) Horizontal Plume Spread Comparison St. Louis Experiment Vertical Plume Spread Comparison Inferred from ground-level concentrations Model Results using stability classes from Lambert Air Field Problems with McElroy-Pooler Curves Using McElroy Pooler curves requires stability and wind speed information. Model results depend on location of measurements. MP curves refer to St. Louis. Need not apply to other urban areas. MP curves implicitly account for the effects of limited mixing. Thus, do not allow the use of mixed layer information in urban areas. Improved Model Model Results using measured meteorology Barrio Logan Experiment Conducted during summer of 2001 resulting in 50 hours of data Sulfur hexafluoride released from ground- level source and measured at distances ranging from 200 m to 2 km using 50 samplers Winds, temperature, and velocity fluctuations measured using sonic anemometers and minisodars Model Results using Boundary Layer Information and Initial Spread Near Source Modeling Model Evaluation Results Conclusions uThe use of McElroy-Pooler curves in all urban areas cannot be justified uTurbulence above the canopy controls dispersion once the plume spread exceeds canopy height. Simple models for dispersion provide adequate concentration estimates provided above canopy meteorology is used uDispersion models should account for magnification of horizontal spread near sources-