The 8-hour average values
above were calculated using all monitoring data. In many instances,
the highest hourly average concentrations occur outside of the
EPA-defined "ozone season." The Yellowstone National
Park site (see blue arrow above) is heavily influenced by natural
sources of ozone. The highest hourly average concentrations occur
at this site during the springtime. Many of the sites shown above
are also affected by natural background ozone. Note that the
8-hour average values are much higher than EPA anticipated for
those sites whose values are heavily influenced by natural background.
For more information, please email us.