A study of the spatial variability of ozone and other pollutants at St Louis, Missouri

Abstract

A network of 25 aerometric stations was part of the U.S. Environmental Protection Agency's Regional Air Pollution Study (RAPS) in the Greater St Louis area. At these stations ozone (O 3) and various other photochemical pollutants [NO, NO 2, and total hydrocarbons (THC)] as well as carbon monoxide (CO) were analyzed with respect to their spatial variability. Data were analyzed for the warm months of the year, April–October 1975 and 1976 — periods during which high O 3 concentrations are common. The results of these analyses indicate that when O 3 concentrations are high (above 100 ppb) the daily 1-h maximum O 3 concentration is highly dependent upon the location of measurement. Measurements made at these times in both urban and rural locations in and around St Louis were frequently found to vary by a factor of 2 and occasionally by a factor as large as 4. Simultaneous hourly average measurements for each of the pollutants were correlated across the network of 25 stations. Rather poor correlations were found for the primary pollutants such as CO, NO, NO 2, and THC. Analysis of normalized fields of pollutant concentrations suggest that the scavenging of O 3 by NO dominates the O 3NO x reaction cycle before 1000 CDT.