Relative Diffusion within the Los Angeles Basin as Estimated from Tetroon Triads

Abstract

The Los Angeles Reactive Pollutant Project (LARPP) in the autumn of 1973 involved helicopter sampling of a volume of air ?tagged? by means of three constant volume balloons (tetroons) released simultaneously from a point on the ground. Based on radar tracking of 35 tetroon triads at a mean height of 350 m above sea level, this paper considers the estimates of relative diffusion obtained from the rate of separation of the tetroons making up the triad. In the average, the median lateral standard deviation of tetroon position varies from 90 m after a travel time of 15 min to 800 m after 2 h, and from 140 m at a travel distance of 2 km to 1000 m at 20 km. The relative diffusion is indicated to be nearly twice as large in ?neutral? as in ?stable? conditions. Comparison with the results obtained by other investigators in other locations shows that the relative diffusion within the Los Angeles Basin is frequently unusually small, particularly with respect to travel time.