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Performance of Air Quality Models in Urban Areas. Akula Venkatram 1 , Vlad Isakov 2 , 1 University of California, Riverside, CA 2 NOAA, NERL, RTP, NC. Objectives and Motivation St. Louis study and ISC urban Model Improvements Performance of Improved Model Conclusions.
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Performance of Air Quality Models in Urban Areas Akula Venkatram1, Vlad Isakov2, 1University of California, Riverside, CA 2NOAA, NERL, RTP, NC • Objectives and Motivation • St. Louis study and ISC urban • Model Improvements • Performance of Improved Model • Conclusions
Motivation and Objectives The most severe air pollution problems in Asia are caused by emissions in urban areas • Examine the performance of currently used urban air quality models-ISC • Suggest 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
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.
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
Conclusions • The use of McElroy-Pooler curves in all urban areas cannot be justified • Turbulence 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 • Dispersion models should account for magnification of horizontal spread near sources- channeling ? • Near source dispersion requires meteorological data close to source, and model needs to incorporate meandering.