On frequency distributions of air pollutant concentrations

Abstract

Observed frequency distributions of air pollutant concentration levels are critically analyzed with respect to their statistical description. It is demonstrated that several common distributions can be used to fit observed data, one of which is the popular log-normal distribution. The observation that concentration distributions for all averaging times are approximately log-normal can be explained if the short averaging time data are themselves assumed to be log-normally distributed. The near log-normality of pollutant concentration frequency distributions can be explained on the basis of the near log-normality of wind speed distributions, although this explanation does not establish that wind speed distributions are solely responsible for observed concentration distributions. It is concluded that pollutant concentration frequency distributions are the result of complex phenomena and cannot be predicted exactly, but that the approximate log-normal character of the distributions is useful from a practical point of view and can be understood qualitatively on the basis of the relation between wind speed and concentration.