Ozone transport in the St. Louis area

Abstract

A network of 25 stations in and around St. Louis, Missouri, continuously recorded wind speed, wind direction, and ozone concentration near the surface as part of the Environment Protection Agency's Regional Air Pollution Study. Data were also obtained on an hourly basis from several pilot-balloon sites within the St. Louis area. These measurements, from July 1 to September 15,1975 and from May 1 to June 19, 1976, were used with annual point and area source emission data in St. Louis to establish some consequences of the local transport of ozone generated within St. Louis. In addition, these data were analyzed in conjunction with synoptic rawinsonde measurements from North America to establish the significance of large-scale ozone transport into the St. Louis area. In rural areas outside of the city ozone concentrations exceeded the National Ambient Air Quality Standard of 80 ppb (160 μ m −3) and could not be attributed to the emissions of pollutants within the metropolitan area of St. Louis. During the period of study this occurred on 15 days when meteorological conditions were conducive to the large-scale transport of ozone. Typically, these high ozone concentrations occurred when the air flowing into St. Louis had been associated with an anticyclone during the 3 days prior to its arrival. Trajectories indicated that during these 3-day periods the air had remained within the eastern half of the United States where there are numerous high-intensity urban-industrial centers. On other days during the study, analyses of the local air flow confirmed that the urban-industrial areas within the immediate vicinity of St. Louis were responsible for high ozone concentration in the city as well as in the rural areas. An analysis of the formation and movement of an “ozone cloud” through the network of stations revealed the consequences of local ozone generation and transport.