Transport and dispersion of airborne pollutants associated with the land breeze-sea breeze system

Abstract

Two atmospheric tracer experiments were conducted in July 1977. Sulphur hexafluoride gas (SF6) was released for a 5-h period during each of two nights from a coastal power plant stack located at the El Segundo Generating Station in the Lot Angeles Basin. The purpose of this study was to investigate the transport and dispersion of plumes released into the land breeze, portion of a land breeze-sea breeze circulation system. Even though a portion of the plume was apparently injected above the base of the night-time inversion, essentially all of the tracer was observed to return across a control surface (from sea level to the base of the inversion) along the coast throughout the sea breeze regime during the following day. The residence time distribution functions of tracer material over the sea were almost identical in both experiments. The average residence time for tracer material over the ocean was 10 h in both cases; however, some of the tracer spent as much as 16 h over the sea. The horizontal dispersion of tracer was also greater than expected, with between 75 and 100 km of coastline impacted by the return of SF6 from a single elevated source. Data from both shipborne and coastal monitoring stations indicated that the path followed by the tracer over the ocean could not have been tracked accurately using trajectories constructed from conventionally available meteorological data.

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