Background Ozone
There is a substantial background of ozone (O3) present in the lower troposphere in the Northern Hemisphere that has both a stratospheric and photochemical tropospheric origin.
Levels of hourly averaged O3 concentrations in the range 0.04 – 0.08 ppm are often measured as part of the “background O3” burden.
Stratospheric processes play a significant role in defining these background O3 concentrations.