What does “reactivity” of emissions mean?
The traditional method of exhaust regulations was to specify the actual HC, CO, NOx, and particulate contents. With the introduction of oxygenates and reformulated gasolines, the volatile organic carbon (VOC) species in the exhaust also changed. The “reactivity” refers to the ozone-forming potential of the VOC emissions when they react with NOx, and is being introduced as a regulatory means of ensuring that automobile emissions do actually reduce smog formation. The ozone-forming potential of chemicals is defined as the number of molecules of ozone formed per VOC carbon atom, and this is called the Incremental Reactivity.
