On the other hand, the upper troposphere is relatively rich in O3 and NOx from natural sources such as downward transport from the stratosphere and lightning; convective overturning conveys the O3 and NOx toward the Earth's surface where these components are more efficiently removed from the atmosphere. (science.sciencemag.org)
Also, the overall number of ozone molecules destroyed in a vertical column of air was pretty much the same as the number of molecules transported into this column by the average poleward and downward transport of air in the stratosphere. (realclimate.org)
When lightning introduces ozone into the upper troposphere, there is some downward transport mechanism that will affect lower tropospheric ozone» Dr. Wang says. (sciencedaily.com)