Large-Scale Weather Influences on Community Air Pollution Potential in the United States

Abstract

This paper describes the large-scale weather features that typically are associated with relatively rapid and slow atmospheric dispersion. Specific examples for some well-known air pollution incidents are illustrated and discussed. Particular attention is paid to the features of quasi-stagnating anticyclones, the typical weather system associated with persistent and extensive areas of sluggish dispersion. On the large scale, the basic quantitative parameters of dispersion over urban areas are the mixing height and the wind speed averaged through that height. These parameters are defined and discussed. Mean morning and afternoon mixing heights and wind speeds are presented for four locations across the United States, illustrating their diurnal, seasonal, and spatial variations. Also for these four locations, data are given on the climatological occurrence of periods during which critical values of the basic parameters were not exceeded. The spatial distributions of mixing heights and average wind speeds during a well-documented air pollution episode are presented.