Articles | Volume 15, issue 20
Atmos. Chem. Phys., 15, 11433–11459, 2015
Atmos. Chem. Phys., 15, 11433–11459, 2015

Research article 16 Oct 2015

Research article | 16 Oct 2015

The MCM v3.3.1 degradation scheme for isoprene

M. E. Jenkin1,2, J. C. Young3, and A. R. Rickard4,5 M. E. Jenkin et al.
  • 1Atmospheric Chemistry Services, Okehampton, Devon, EX20 4QB, UK
  • 2School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK
  • 3School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK
  • 4Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
  • 5National Centre for Atmospheric Science, University of York, Heslington, York, YO10 5DD, UK

Abstract. The chemistry of isoprene degradation in the Master Chemical Mechanism (MCM) has been systematically refined and updated to reflect recent advances in understanding, with these updates appearing in the latest version, MCM v3.3.1. The complete isoprene degradation mechanism in MCM v3.3.1 consists of 1926 reactions of 602 closed shell and free radical species, which treat the chemistry initiated by reaction with OH radicals, NO3 radicals and ozone (O3). A detailed overview of the updates is provided, within the context of reported kinetic and mechanistic information. The revisions mainly relate to the OH-initiated chemistry, which tends to dominate under atmospheric conditions, although these include updates to the chemistry of some products that are also generated from the O3- and NO3-initiated oxidation. The revisions have impacts in a number of key areas, including HOx recycling, NOx recycling and the formation of species reported to play a role in SOA (secondary organic aerosol)-formation mechanisms. The performance of the MCM v3.3.1 isoprene mechanism has been compared with those of earlier versions (MCM v3.1 and MCM v3.2) over a range of relevant conditions, using a box model of the tropical forested boundary layer. The results of these calculations are presented and discussed and are used to illustrate the impacts of the mechanistic updates in MCM v3.3.1.

Short summary
Atmospheric isoprene oxidation has an important effect on the formation of pollutants such as ozone and particles. A reliable representation is an essential component of climate change/air quality models. Systematic updates to the detailed chemistry in the MCM are described, with reference to recently reported kinetic/mechanistic data. Results of box model calculations are used to illustrate the impacts of the updates, with particular focus on the key atmospheric cycles involving HOx and NOx.
Final-revised paper