Note the reactions labeled 1, 2 and 3 in the diagram. All three of these reactions occur at all times during daylight hours. Reaction 1 which is driven by sunlight creates ozone, while reactions 2 and 3 consume ozone. Reaction 3 depends on NOx to do its job. In certain cases if NOx levels are reduced less ozone is consumed by reaction 3, and reaction 1 drives ozone levels higher. These higher levels of ozone are called the "disbenefits"of NOx reduction.