EFFECTS OF CHEMICAL MECHANISM UNCERTAINTIES ON THE REACTIVITY QUANTIFICATION OF VOLATILE ORGANIC-COMPOUNDS USING A 3-DIMENSIONAL AIR-QUALITY MODEL

Accurate quantification of the ozone-forming potential, termed ''react ivity'', of volatile organic compounds (VOCs) is critical for correctl y assessing the impacts of emissions on air quality. As reactivity-bas ed regulations are being more carefully considered for urban ozone con trol strategies, the uncertainties in our ability to quantify reactivi ty are gaining importance. This study utilized a three-dimensional air quality model to examine the uncertainty in reactivity quantification resulting from a set of reaction rate constant uncertainties. A previ ous study identified the set of rate constants that were most critical for single-cell model ozone predictions. With the detailed airshed mo del, uncertainties in rate constants for aldehyde photolysis, nitric a cid formation, and decomposition of peroxy acetyl nitrate (PAN) and pe roxy propionyl nitrate plus higher PAN analogues (PPN) exhibited the g reatest impact on relative compound reactivity values. For the compoun ds and reactions examined, the combined responses to 2 sigma changes i n reaction rate constants were approximately 15% of the predicted rela tive reactivity values, with the reactivities of ethylbenzene and tolu ene exhibiting the greatest response. The choice of reactivity quantif ication measures and the air quality models used had a greater impact on relative reactivity predictions than did the rate constant uncertai nties.