Analysis of Los Angeles Photochemical Smog Data: A Statistical Overview

A research project has been under way to investigate air pollution problems in Los Angeles County with the help of the data supplied by the Los Angeles County Air Pollution Control District. These data consist of measurements of primary pollutants such as nitric oxide, hydrocarbons, carbon monoxide, sulfur dioxide and particu-lates, and secondary pollutants such as ozone and nitrogen dioxide, recorded hourly at a number of different stations in Los Angeles County over the past seventeen years. This present discussion deals in a preliminary way with a particular aspect of this analysis, namely, the occurrence of photochemical smog in Los Angeles. The paper is divided into two main sections. The first is intended to provide a brief survey of the problem of photochemical smog in Los Angeles as presently understood in relation to the available field data and also in relation to chamber experiments which have been run in various laboratories. The second part of the paper discusses a class of intervention problems that arise in studying the data. It is noted that parallel problems occur in the study of other ecological material and elsewhere. Statistical methods for dealing with this class of problems are illustrated with some of the Los Angeles data.