RELATIONSHIPS BETWEEN DIRECTION OF WIND FLOW AND OZONE INFLOW CONCENTRATIONS AT RURAL LOCATIONS OUTSIDE OF ST-LOUIS, MO

The relationships between the monthly and seasonal averages of the daily 1200-1500 h O3 inflow concentrations and wind flow direction have been evaluated. The O3 measurements used are those during inflow of air parcels from upwind to rural monitoring stations outside of St. Louis, MO. The results obtained are consistent with the O3 measurements reported from other monitoring studies at rural locations both to the west and east of St. Louis. Although there is a stratospheric component to these ground level rural O3 concentrations, it is likely that most of the O3 measured during the warmer months of the year is associated with photochemical O3 formation in the planetary boundary layer and in the free troposphere. A substantial part of the increments in rural O3 concentrations which occur from west to east of St. Louis during the warmer months of the years appear best to be accounted for as a result of photochemical formation O3 precursors from anthropogenic emission sources to the east of St. Louis. Differences in the values of meteorological parameters with wind flow direction account for only a small part of the differences in O3 concentration observed.