The new approach could save tens of millions of dollars while attaining VOC reductions equal to or greater than what is achieved currently. A New Approach Thirty miles above the Earth, the ozone layer protects living things by filtering out the Sun's damaging ultraviolet rays. Earth-bound ozone offers no such benefit. The problem occurs when hydrocarbons, a class of VOCs, react in the atmosphere with nitrogen oxides, a combustion byproduct. Mixed by winds and cooked by the sun, they combine to create smog.
Automobile exhaust is a primary culprit, simultaneously spewing hydrocarbons and nitrogen oxides.
By offering a means to compare VOC reactivity levels in like products, such as gasolines, a reactivity scale can weigh the ozone-causing potential of one VOC source against another. Each VOC is assigned a value that reflects the amount of ozone it will produce. But design depends on the urban setting in question and the level of nitrogen-oxide emissions expected, so a scale for Los Angeles, for instance, might not be useful for New York. Despite atmospheric differences among cities, says Russell, data suggest differences in VOC reactivities across the nation tend to balance one another out. Using existing scales as a springboard.