ANALYSIS OF TRACER DATA FROM URBAN DISPERSION EXPERIMENTS Akula Venkatram and Vlad Isakov  Motivation for Field Experiments  Field Studies Conducted in Barrio Logan  Results from Current Models  New Modeling Approach  Results  Future Work

Motivation u Few experiments conducted for ground-level releases in urban areas. –St Louis Experiment in 1968 u Little data for near source dispersion u Data set is specific to Barrio Logan

Urban Effects on Dispersion Stable air from the rural area becomes unstable when it flows over warmer urban area Roughness increases turbulence and decreases wind speed

Field Experiments Tracer studies designed to study dispersion at scales of meters to kilometers in urban areas. –Near source experiment at Memorial High, April 2001 –CE-CERT parking lot study, April-May 2001 –Summer and winter Barrio Logan field studies –Dugway Proving Grounds Model Study

Near Field Dispersion-tens of meters SF 6 released at ground level in a school playground in an urban area u Source surrounded by two arcs at 10 and 20 meters u Flow measured with sonics, propeller anemometers, and mini-sodar u Real time analysis of data

Near source dispersion  v is comparable to effective wind speed transporting plume u Upwind dispersion becomes important u Plume model might not be applicable

Near Field Dispersion Experiment at BL Memorial School (April 7 – 14, 2001)

Concentration Pattern on 4/14/01

Concentration Pattern on 4/13/01

Concentration Pattern on 4/12/01

CE-CERT Parking Lot

CE-CERT Model Comparison

Low Wind Speed Model The horizontal distribution is written as:

Tracer Experiment at Barrio Logan l Tracer Experiment conducted in August and December of 2001 l Hourly SF6 concentrations sampled at 50 sites l Tracer released at NASSCO during daytime from 10 a.m. to 10 p.m. l Mobile van sampled continuously to measure crosswind SF6 concentrations l Mini-sodar to measure vertical winds up to 200m at 5m resolution l Six sonic anemometers to measure surface level winds and turbulence

Logan Memorial Wind Rose Nov 1, 1999 to Oct 31, 2000 Sea Breeze (predominately daytime) Land Breeze (predominately nighttime)

Map of Barrio Logan tracer experiment August 2001 yellow dotd - stationary samplers black lines - mobile van locations

Model Performance at 200m on 08/21/2001

Model Performance at 500m on 08/21/2001

Model Performance at 1000m on 08/21/2001

Model Performance at 2000m on 08/21/2001

Model Performance at 200m on 08/25/2001

Model Performance at 500m on 08/25/2001

Model Performance at 1000m on 08/25/2001

Model Performance at 2000m on 08/25/2001

Q-Q Plots for Model Results from 5 days

Model for Urban Areas u Micrometeorological variables used to describe flat terrain dispersion do not apply to urban areas u Formulate model that uses measured turbulence and velocity profiles

Model for Plume Spread

Comparison with Prairie Grass Data

Model Field Study u Understand dispersion in flat terrain at distances of less than 50 m u Examine the effect of increasingly complicated building structures on –Turbulence –Dispersion

Model Field Study u Conducted at Dugway Proving Ground, Utah July 17,18,19, u 13.5 hours under a variety of stability conditions u Velocity and turbulence measured with sonic anemometers u Buildings simulated with barrels

Model Urban Area u 5  9 array of 45 barrels u H=0.91 m and D=0.57 m at spacing of 1.8 m- frontal area/plan area=16% u Propylene released at z=0 and z=H u 6 different configurations to examine the effect of release height and source structure

Concentration Measurements u Tracer measured with 43 PIDs arranged in 3, 50 degree arcs u Arcs at 1.5S, 2.5S, and 4.5S u PIDs at 5 o spacing u PIDs located at z=0.23 m u Four 2 m towers were used to measure vertical profiles u Concentrations measured at 50 Hz

Meteorological Measurements u Turbulence measured with 6 sonics u Sonics mounted on 3 and 5 m towers u Mounted at 0.5, 1.5, 2.2 and 3.5H at various distances from the source u Measurements at 20 Hz

Figure 2. Observed versus Predicted concentration using model plume spreads without obstacle for ground level release

Figure 3. Observed versus Predicted concentration using linear plume spreads with one obstacle in array for ground level release

Figure 4. Observed versus Predicted concentration using model plume spreads with one obstacle in array for ground level release

Figure 6. Observed versus Predicted concentration using model plume spreads with two obstacles in array for ground level release

Future Work u Model might require modification to account for source effects u Need to account for plume meandering-upwind dispersion u Need to evaluate model with CE- CERT data and Barrio Logan winter data