Reactive organic gases (ROG) undergo a series of reactions to form radicals (compounds with an open hydrogen bond; they are highly reactive). The alkylperoxy radical (RO2*) reacts with and oxidizes NO to form NO2 faster than NO reacts with O3 to produce the same result. Thus, when ROGs are present, it is likely that O3 will not be destroyed to produce NO2. The null cycle is not "null" anymore. Note that each time an NO2 molecule is formed (by whatever method), it very quickly results in the production of O3 (via photodissociation and a recombination).

This diagram shows the relevant step from the ROG cycle (RO2* + NO -> NO2 + RO*) added to the null cycle shown in an earlier screen. The O3 now reaches a dead end (the ozone molecule now has a longer residence time, since it must undergo a slower reaction with some other substance instead of being quickly used up to oxidize nitric oxide).