1School of Earth & Environment, University of Leeds, Leeds, UK
2School of Chemistry, University of Leeds, Leeds, UK
3National Centre for Atmospheric Science, University of Leeds, Leeds, UK
4Department of Chemistry, University of Leicester, Leicester, UK
5Department of Chemistry, University of York, York, UK
6National Centre for Atmospheric Science, University of York, York, UK
7School of Environmental Sciences, University of East Anglia, Norwich, UK
8National Centre for Atmospheric Science, University of East Anglia, Norwich, UK
*now at: School of Engineering & Applied Sciences, Harvard University, Cambridge, USA
**now at: Department of Chemistry, University of Reading, Reading, UK
Received: 16 Mar 2011 – Discussion started: 31 Mar 2011
Abstract. Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO2 in airmasses impacted with isoprene are 5.32−4.43+3.68 and 1.18−0.30+0.30 respectively, with 68 % of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.
Revised: 08 Jun 2011 – Accepted: 04 Jul 2011 – Published: 14 Jul 2011
Stone, D., Evans, M. J., Edwards, P. M., Commane, R., Ingham, T., Rickard, A. R., Brookes, D. M., Hopkins, J., Leigh, R. J., Lewis, A. C., Monks, P. S., Oram, D., Reeves, C. E., Stewart, D., and Heard, D. E.: Isoprene oxidation mechanisms: measurements and modelling of OH and HO2 over a South-East Asian tropical rainforest during the OP3 field campaign, Atmos. Chem. Phys., 11, 6749-6771, doi:10.5194/acp-11-6749-2011, 2011.