The analysis of data from an urban dispersion experiment

This paper describes the design and implementation of a field study to understand dispersion in an urban area, characterized by buildings whose heights are less than 5 m. The study site, Barrio Logan, is located on the San Diego shore line, where most of the industry is located. The predominant wind from the SW brings emissions from the industrial area into the residential area located downwind in the NW. The field study was conducted during the period 21–31 August 2001 on 5 days. The tracer, SF6, was released at a height of 5 m from a shipyard on the shoreline, and the concentrations of the tracer were sampled on four arcs at 200, 500, 1000, and 2000 m from the source during 10 h of each day starting at 10 am. This experiment was designed to provide data during both daytime and nighttime conditions. The meteorological conditions that governed dispersion were measured using sonic anemometers and a SODAR with a range of 200 m in the vertical. The maximum concentrations (normalized by the emission rate) measured during the experiments ranged from 100 μs m−3 at 200 m to 1 μs m−3 at 2000 m. An analysis of the concentration observations indicated that the maximum concentrations followed: where the dilution velocity is given by Udil, a measure of the dilution capability of the boundary layer, varied between 0.1 and 0.2 m s−1 during most of the field study hours.