One of the factors that causes this paradox is the way in which ozone moves in the atmosphere, specifically in the lower and middle troposphere. Another contributor to the higher ozone levels is lightning, because it causes a chemical reaction in the atmosphere that leads to the formation of ozone. The converging winds mix the lower level ozone and other pollutants from north to south, and are responsible in part for this paradox. The northern trade winds transported the pollutants from northern equatorial Africa and contributed to the tropical Southern Hemisphere ozone maximum. The Lightning Imaging Sounder onboard the TRMM satellite detected the frequency of lightning in the Southern Hemisphere where ozone levels were highest.
Lightning produces nitric oxide that in turn leads to rapid ozone formation.
Significant lightning activity was observed in the Southern Hemisphere over Africa, which contributed to the higher ozone concentration in the troposphere. NASA instruments have been measuring ozone levels since the early 1970s. TOMS has been a key instrument for monitoring ozone levels over the Earth.