ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-2751-2009 Mainz Isoprene Mechanism 2 (MIM2): an isoprene oxidation mechanism for regional and global atmospheric modelling Taraborrelli D. 1 Lawrence M. G. 1 Butler T. M. 1 Sander R. 1 Lelieveld J. 1 Max Planck Institute for Chemistry, Atmospheric Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany 27 04 2009 9 8 2751 2777 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/2751/2009/acp-9-2751-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/2751/2009/acp-9-2751-2009.pdf

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<sub>x</sub> regimes. We evaluate MIM2 and re-evaluate MIM through comparisons with MCM v3.1. We find that MIM and MIM2 compute similar O<sub>3</sub>, OH and isoprene mixing ratios. Unlike MIM, MIM2 produces small relative biases for NO<sub>x</sub> and organic nitrogen-containing species due to a good representation of the alkyl and peroxy acyl nitrates (RONO<sub>2</sub> and RC(O)OONO<sub>2</sub>). Moreover, MIM2 computes only small relative biases with respect to hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), methyl peroxide (CH<sub>3</sub>OOH), methanol (CH<sub>3</sub>OH), formaldehyde (HCHO), peroxy acetyl nitrate (PAN), and formic and acetic acids (HCOOH and CH<sub>3</sub>C(O)OH), being always below &asymp;6% in all NO<sub>x</sub> 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 CO<sub>2</sub> as well. Therefore, it is suitable for studies assessing carbon monoxide (CO) from biogenic sources, as well as for studies focused on the carbon cycle. Compared to MIM, MIM2 considers new species like acetaldehyde (CH<sub>3</sub>CHO), propene (CH<sub>2</sub>=CHCH<sub>3</sub>) and glyoxal (CHOCHO) with global chemical production rates for the year 2005 of 7.3, 9.5 and 33.8 Tg/yr, respectively. Our new mechanism is expected to substantially improve the results of atmospheric chemistry models by representing many more intermediates, that are transported and deposited, which allows us to test model results with many more new measurements. MIM2 allows regional and global models to easily incorporate new experimental results on the chemistry of organic species.

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