Forecasting the Behavior of the St. Louis, Missouri, Pollutant Plume

Forecasts of the position and structure of the St. Louis pollutant plume became necessary during the NCAR Fate of Atmospheric Pollutants Study (FAPS). The purpose of the project was to obtain estimates of the mean lifetimes of a number of short-lived pollutants by taking measurements at distances of 80 and 120 km from the Gateway Arch. Determining where and when to make such measurements at a reasonable cost involved assessing the interaction of the pollutants from the city with the atmosphere. This paper describes the concepts used by the meteorologist to help anticipate the variation of the plume in space and time, including its diurnal variation, in weather conditions considered favorable for sampling. The plume models that evolved from these concepts are presented, and a comparison is made of the actual behavior of the plume as determined from measured concentrations of the pollutants with the behavior predicted by the models. The comparison shows good agreement.