Characteristics of Summer Midday Low-Visibility Events in the Los Angeles Area

■ A five-site air monitoring network provided data during the summer of 1984 on pollutants that contribute to the midday visibility problem in the Los Angeles area. The data were supplemented by visual range observations and by nephelometer measurements of total light scattering. The network collected data over an extended region, obtained a data set describing the frequency distribution of high- and low-visibility events over an extended time period, and obtained information needed to calculate the cause and effect relationship between pollutant properties and the extinction coefficient from theories of light scattering and absorption, rather than from statistical techniques. Computed scattering coefficient values at the Pasadena site are on average within 26% of the measured values. Frequency distributions of calculated extinction coefficients at Pasadena agree with the frequency distribution of extinction coefficients estimated from visual range values for all but the extreme extinction cases. These data can be used to investigate the effect that an emission control program would have on visibility in the Los Angeles area.