Some characteristics of ozone formation in the urban plume of St. Louis, MO

Abstract

The O 3 measurements from the Regional Air Monitoring System (RAMS) in St. Louis in the upwind and downwind flow directions have been used to evaluate the first day impact of the urban plume of St. Louis. The time periods between April and October 1975 and 1976 have been utilized for this purpose. Ozone formation in the urban plume has been evaluated with respect to the distribution of O 3 concentrations at RAMS stations downwind. The relationships between O 3 concentrations in the urban plume and such meteorological parameters as wind direction, wind speed, temperature, solar radiation intensity and maximum mixing heights have been investigated. Plume widths also have been estimated and related to plume O 3 intensities. Incremental O 3 formation within the urban plume compared to regional O 3 background increases both in frequency and intensity from spring into midsummer and declines again in late summer and early fall. Episodic periods with substantial increments of O 3 formation in the plume over background occur especially during the summer months. Aircraft measurements of O 3 in the St. Louis plume are discussed by considering first day transport distances, plume widths and O 3 profiles beyond the outer stations in the RAMS network. The significance of incremental O 3 formation is evaluated in the St. Louis plume on population exposures as well as on fumigations of field crops or forest in rural areas downwind. The strongest effects of O 3 formation in the plume occur in the prevailing wind direction. The O 3 in the plumes from all of the cities in an interior region of the U.S. is estimated to impact 5–10% of the rural lands in this region on any given day.