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CONDENSED ATMOSPHERIC PHOTOOXIDATION MECHANISMS FOR ISOPRENE by William P L Carter Atmospheric Environment in press February 22 1996 Statewide Air Pollution Research Center and College of Engineering Center for Environmental Research and Technology University of California Riverside CA 92521 ABSTRACT Two condensed mechanisms for the atmospheric reactions of isoprene which differ in the number of species used to represent isoprene s reactive products have been developed for use in ambient air quality modeling They are based on a detailed isoprene mechanism that has recently been developed and extensively evaluated against environmental chamber data The new condensed mechanisms give very close predictions to those of the detailed mechanism for ozone OH radicals nitric acid H2O2 formaldehyde total PANs and for incremental effects of isoprene on for ozone formation in one day simulations The effects of the condensations become somewhat greater in multi day simulations particularly in cases where NO3 reactions are important at nighttime but the ozone predictions are still very close On the other hand the SAPRC 90 RADM 2 and Carbon Bond IV isoprene mechanisms give quite different predictions of these quantities It is recommended that the new mechanisms replace those currently used in airshed simulations where isoprene emissions are important Keywords Isoprene Airshed Models Chemical Mechanisms Photochemical Smog Ozone Air Quality Methacrolein Methyl Vinyl Ketone Biogenic Hydrocarbons INTRODUCTION Isoprene is emitted from certain types of vegetation and is believed to play an important role in both urban and rural ozone formation Trainer et al 1987 Chameides et al 1988 Sillman et al 1990 For this reason its reactions are represented in most of the currently used urban or regional air quality models For example the Carbon Bond IV CB4 Gery et al 1988 RADM 2 Stockwell et al 1990 or SAPRC 90 Carter 1990 Lurmann et al 1991 chemical mechanisms which are widely used in airshed

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