The third dimension in the Los Angeles basin

Abstract

Airborne measurements were made during the summer and early fall seasons of 1978–1980 to characterize the third dimension of the Los Angeles Basin during air pollution days. One to three aircraft were employed per flight day to measure the vertical profile of meteorology and air quality continuously, and to collect aerosol samples for the various chemical analyses across the Basin. Particular emphasis was placed in the nighttime measurements. This was done because relatively little nighttime third dimension data are available to date, and because they are important in defining the initial conditions for the following photochemically active days. It was found that the physical and chemical characteristics within the two meteorological regimes, i.e., mixed and stable layers, are distinctively different. The mixed layer is characterized by uniformly low O 3 and relatively high NO x at night, while he stable layer has stratified high O 3 but low NO x. Aerosol size distribution in the mixed layer is found to be tri-modal, while that in the stable layer is nearly bi-modal. Based on the collected data, the nighttime sulfur, nitrate and ammonia chemistry is discussed.