Development and Application of Dual Atmospheric Tracer Techniques for the Characterization of Pollutant Transport and Dispersion

Author: Lamb, Brian Kent

Year: 1978

Degree: Dissertation (Ph.D.)

Advisor: Shair, Fredrick H.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/6djp-n724

Abstract

Environmental concerns over urban development and industrial growth have resulted in increased interest in atmospheric tracers. Expanding urban areas in coastal regions make it particularly important to understand the effects of complex meteorological patterns and rough terrain upon the transport and dispersion of atmospheric pollutants. The purpose of this thesis was to further develop single and double atmospheric tracer techniques which would be economical and efficient for large-scale field studies. Sulfur hexafluoride and bromo-trifluoromethane were selected as tracers since they are both inert gases detectable by electron capture gas chromatography in the parts per trillion range . A tracer system was developed which permitted the collection and analysis of as many as 1000 air samples per day. This system was then used to demonstrate the application of tracer techniques to important problems of current interest in both coastal and noncoastal zones over distances as great as 100 km.

Atmospheric tracer studies, conducted in Southern California during September, 1975, investigated the possible transport of pollutants between the Los Angeles Basin and the Oxnard Plain. The SF6 data clearly showed that pollutant transport occurs from the Oxnard Plain along the Malibu coast into the Los Angeles Basin.

A second series of tracer studies using SF6 and CBrF3 were completed within the California Delta Region during September, 1976. The purpose of these tests was to analyze the impact of possible industrial developments in the Montezuma Hills of the Delta Region. The relative impact of existing and proposed industrial sources was investigated by simultaneously releasing CBrF3 from the Montezuma Hills and SF6 from upwind of the Delta Region. Results indicated that plumes from both areas were carried southeast over Stockton into the San Joaquin Valley.

Data from both of the coastal studies indicated that because of periods of steady coastal winds, the commonly used Hino correction grossly underestimated hourly averaged concentrations computed from 10-second averaged concentrations. Tracer concentrations predicted from the Gaussian plume model overestimated values observed in the Oxnard study because of increased dispersion over rough terrain. Predicted concentrations showed good agreement with observed values in the Delta study where the terrain was relatively flat. When sufficient data were available, surface air parcel trajectories determined from numerical solutions of the two-dimensional conservation equation were found to be more accurate than trajectories drawn from meteorological streamline maps.

Five large-scale tracer studies utilizing SF6 and CBrF3 were performed in urban St. Louis during August, 1975, to probe the relative impact of emissions from low-level and elevated sources. Releases of SF6 were used to simulate elevated sources, while simultaneous releases of CBrF3 were used to simulate low-level sources. The dispersion of emissions from low-level sources was initially enhanced in contrast to the dispersion of emissions from elevated sources.

Analysis of the St. Louis t racer data resulted in the development of the concept of a limit model of air quality. By considering the relative impact of different sources and formulating necessary assumptions in terms of an upper or lower bound , the limit model approach offers a new perspective upon contemporary air quality problems. The application of this concept was demonstrated in the development of an upper limit model of the relative impact of elevated rural sources and low-level urban sources upon urban SO2 levels in St. Louis. Results of this application indicated that rural sources contribute no more than 25% of the average total urban SO2 concentration, even though rural sources can dominate urban air quality in portions of the urban region during relatively large portions of the time.

As a means of applying experience gained from atmospheric tracer studies to liquid systems, a method was developed for the determination of the solubility of halogenated compounds in liquids. Solubilities of SF6 in water measured with this technique were in good agreement with literature values. The method was used to determine, for the first time, values of the solubility of SF6 in a homologous series of n-alcohols. The method allows SF6 to be used as a tracer in a number of unique liquid systems including the characterization of the interfacial exchange rate of gases across the pulmonary membrane of the lung.

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