A NEW MECHANISM FOR REGIONAL ATMOSPHERIC CHEMISTRY MODELING

A new gas-phase chemical mechanism for the modeling of regional atmosp heric chemistry, the ''Regional Atmospheric Chemistry Mechanism'' (RAC M) is presented. The mechanism is intended to be valid for remote to p olluted conditions and from the Earth's surface through the upper trop osphere. The RACM mechanism is based upon the earlier Regional Acid De position Model, version 2 (RADM2) mechanism [Stockwell et al., 1990] a nd the more detailed Euro-RADM mechanism [Stockwell and Kley, 1994]. T he RACM mechanism includes rate constants and product yields from the most recent laboratory measurements, and it has been tested against en vironmental chamber data. A new condensed reaction mechanism is includ ed for biogenic compounds: isoprene, alpha-pinene, and d-limonene. The branching ratios for alkane decay were reevaluated, and in the revise d mechanism the aldehyde to ketone ratios were significantly reduced. The relatively large amounts of nitrates resulting from the reactions of unbranched alkenes with NO3 are now included, and the production of HO from the ozonolysis of alkenes has a much greater yield. The aroma tic chemistry has been revised through the use of new laboratory data. The yield of cresol production from aromatics was reduced, while the reactions of HO, NO3, and O-3 with unsaturated dicarbonyl species and unsaturated peroxynitrate are now included in the RACM mechanism. The peroxyacetyl nitrate chemistry and the organic peroxy radical-peroxy r adical reactions were revised, and organic peroxy radical + NO3 reacti ons were added.