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Investigation of Atmospheric Dispersion Problems by Means of a Tracer Technique


Drivas, Peter John (1975) Investigation of Atmospheric Dispersion Problems by Means of a Tracer Technique. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/e0az-n959.


The purpose of this thesis was to extend the capabilities of an existing atmospheric tracer technique and to demonstrate the sensitivity and usefulness of this technique by investigating a number of complex atmospheric dispersion problems. These problems ranged from a fairly small scale of about one meter to a quite large scale of about 100 kilometers. The tracer used was sulfur hexafluoride, an inert non-toxic gas detected by means of electron-capture gas chromatography; the air sampling and analysis techniques were developed to permit a minimum detection limit of one part SF6 in 1012 parts of air. Four main atmospheric dispersion problems of environmental significance were studied in detail: ventilation systems in buildings; air flow within the wake downwind of a building; dispersion from an urban highway; and largescale transport and dispersion over the Los Angeles area.

Tracer experiments involving SF6 were used to obtain quantitative data regarding actual residence time distributions in rooms and hallways, and contamination caused by reentry of laboratory fume hood hood exhausts into a building. Application of a mixing factor was found useful in room ventilation tests, and measured values ranged from 0.3 to 0.7 in small rooms without fans. In one experiment with a roof fume hood exhaust located only 16 feet from the main ventilation intake of a building, 20% of the fumes exhausted were found to reenter the ventilation system.

Sulfur hexafluoride was used to probe the air flow within the wake downwind of a 12 meter high, three-story building. A reverse-flow circulation was observed with a longitudinal extent downwind of about three building heights; the extent of the recirculation on the roof was confined to less than one-half the width of the building from the downwind edge. The recirculating velocities in the wake were estimated to be about 0.1 - 0.3 those of the prevailing wind at the top of the building. The wake downwind of the building was found to be well-mixed in all three dimensions and exhibited a characteristic exponential dilution time of approximately one minute.

A number of quasi-instantaneous line source releases of SF6 were made by an automobile moving along an urban highway in Los Angeles. Concentrations at various distances from 0.4 km to 3.2 km downwind of the highway were recorded at ground level as a function of time. The tracer data were used to test the validity of several theoretical models which can be used in predicting the dispersion from an instantaneous crosswind line source. The model based upon the semi-empirical turbulent diffusion equation, using a power-law vertical velocity profile and a power-law vertical eddy diffusivity profile, was found to provide the best agreement with the data.

Finally, sulfur hexafluoride was used as a tracer in a large-scale test over the urban region near Los Angeles. On July 19, 1973, 33.5 kg of SF6 was released over a period of 45 minutes from the city of Anaheim. The transport and dispersion from Anaheim was traced in five neighboring communities including Palm Springs, which at 124 km away was the furthest location tested. A preliminary analysis of the data indicated that the cities of Riverside and Palm Springs possibly lie in a direct path of the pollutant transport from Anaheim.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemical Engineering
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Shair, Fredrick H.
Thesis Committee:
  • Shair, Fredrick H. (chair)
Defense Date:24 June 1974
Funding AgencyGrant Number
Ford FoundationUNSPECIFIED
Record Number:CaltechTHESIS:10262021-223635283
Persistent URL:
Related URLs:
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Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14405
Deposited By: Benjamin Perez
Deposited On:27 Oct 2021 23:51
Last Modified:27 Oct 2021 23:52

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