This page last reviewed January 27, 2016
An advisory board was formed, and recommended the use of reactivity to adjust the weight of emissions so that the limits reflect the ozone-forming potential of the emissions rather than the simple mass. The Low Emission Vehicle/Clean Fuels regulation, which was adopted in 1990, uses Reactivity Adjustment Factors (RAF) to set the limits on vehicle emissions. A RAF2 is the ratio of the exhaust reactivity of the alternative fueled vehicle to the exhaust reactivity of the conventionally fueled vehicle. The exhaust reactivity is calculated by taking the sum of the mass fraction of each compound times the reactivity of the compound summed over all the compounds in the exhaust.
As such, it complements ARB's NOx control program, which is designed to reduce ozone under conditions that are sensitive to NOx reductions. Another issue was the degree of uncertainty in the RAFs. Because RAFs are ratios of reactivities, they are similar to relative reactivities. A number of studies have found that relative reactivities have much smaller uncertainties than absolute reactivities. Work done by Yang and Milford found that uncertainties in RAFs are on the order of 15%, while uncertainties in the associated MIRs values were closer to 30 to 70%.
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For questions concerning ARB's Reactivity Program, please contact Dongmin Luo at (916) 324-8496