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Performance of Air Quality Models in Urban Areas  Objectives and Motivation  St. Louis study and ISC urban  Model Improvements  Performance of Improved.

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Presentation on theme: "Performance of Air Quality Models in Urban Areas  Objectives and Motivation  St. Louis study and ISC urban  Model Improvements  Performance of Improved."— Presentation transcript:

1 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 Venkatram 1, Vlad Isakov 2, 1 University of California, Riverside, CA 2 NOAA, NERL, RTP, NC

2 Motivation and Objectives The most severe air pollution problems in Asia are caused by emissions in urban areas u Examine the performance of currently used urban air quality models-ISC u Suggest improvements based on recent tracer studies in urban areas

3 St. Louis Experiment  Conducted during 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

4 McElroy-Pooler Curves Briggs(1974)

5 Horizontal Plume Spread Comparison St. Louis Experiment

6 Vertical Plume Spread Comparison Inferred from ground-level concentrations

7 Model Results using stability classes from Lambert Air Field

8 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.

9 Improved Model

10 Model Results using measured meteorology

11 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

12 Model Results using Boundary Layer Information and Initial Spread

13 Near Source Modeling

14 Model Evaluation Results

15 Conclusions u The use of McElroy-Pooler curves in all urban areas cannot be justified u 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 u Dispersion models should account for magnification of horizontal spread near sources- channeling ? u Near source dispersion requires meteorological data close to source, and model needs to incorporate meandering.


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