Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 8 2009 10.5194/acp-9-2751-2009 http://www.atmos-chem-phys.net/9/2751/2009/ http://www.atmos-chem-phys.net/9/2751/2009/acp-9-2751-2009.html http://www.atmos-chem-phys.net/9/2751/2009/acp-9-2751-2009.pdf 2751 2777 2009-04-27 Mainz Isoprene Mechanism 2 (MIM2): an isoprene oxidation mechanism for regional and global atmospheric modelling D. Taraborrelli tara@mpch-mainz.mpg.de M. G. Lawrence T. M. Butler R. Sander J. Lelieveld Max Planck Institute for Chemistry, Atmospheric Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany We present an oxidation mechanism of intermediate size for isoprene (2-methyl-1,3-butadiene) suitable for simulations in regional and global atmospheric chemistry models, which we call MIM2. It is a reduction of the corresponding detailed mechanism in the Master Chemical Mechanism (MCM v3.1) and intended as the second version of the well-established Mainz Isoprene Mechanism (MIM). Our aim is to improve the representation of tropospheric chemistry in regional and global models under all NO_x regimes. We evaluate MIM2 and re-evaluate MIM through comparisons with MCM v3.1. We find that MIM and MIM2 compute similar O₃, OH and isoprene mixing ratios. Unlike MIM, MIM2 produces small relative biases for NO_x and organic nitrogen-containing species due to a good representation of the alkyl and peroxy acyl nitrates (RONO₂ and RC(O)OONO₂). Moreover, MIM2 computes only small relative biases with respect to hydrogen peroxide (H₂O₂), methyl peroxide (CH₃OOH), methanol (CH₃OH), formaldehyde (HCHO), peroxy acetyl nitrate (PAN), and formic and acetic acids (HCOOH and CH₃C(O)OH), being always below ≈6% in all NO_x scenarios studied. Most of the isoprene oxidation products are represented explicitly, including methyl vinyl ketone (MVK), methacrolein (MACR), hydroxyacetone and methyl glyoxal. MIM2 is mass-conserving with respect to carbon, including CO₂ as well. 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