ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-169-2010 Overview: oxidant and particle photochemical processes above a south-east Asian tropical rainforest (the OP3 project): introduction, rationale, location characteristics and tools Hewitt C. N. 1 Lee J. D. 2 MacKenzie A. R. 1 Barkley M. P. 3 Carslaw N. 4 Carver G. D. 5 Chappell N. A. 1 Coe H. 6 Collier C. 7 Commane R. 8 18 Davies F. 7 Davison B. 1 DiCarlo P. 9 Di Marco C. F. 10 Dorsey J. R. 6 Edwards P. M. 8 Evans M. J. 11 Fowler D. 10 Furneaux K. L. 19 21 Gallagher M. 6 Guenther A. 12 Heard D. E. 8 Helfter C. 10 Hopkins J. 13 Ingham T. 8 Irwin M. 6 Jones C. 13 Karunaharan A. 14 Langford B. 1 Lewis A. C. 13 Lim S. F. 15 MacDonald S. M. 8 Mahajan A. S. 8 Malpass S. 4 McFiggans G. 6 Mills G. 16 Misztal P. 10 17 Moller S. 13 Monks P. S. 14 Nemitz E. 10 Nicolas-Perea V. 14 Oetjen H. 8 Oram D. E. 16 Palmer P. I. 3 Phillips G. J. 10 Pike R. 5 Plane J. M. C. 8 Pugh T. 1 Pyle J. A. 5 Reeves C. E. 16 Robinson N. H. 6 Stewart D. 16 20 Stone D. 8 11 Whalley L. K. 8 Yin X. 5 Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK National Centre for Atmospheric Science, University of York, York YO10 5DD, UK School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JW, UK Environment Department, University of York, York YO10 5DD, UK Centre for Atmospheric Science, Department of Chemistry, Cambridge University, Cambridge, CB2 1EW, UK School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 3PL, UK Centre for Environmental Systems Research, University of Salford, Salford M5 4WT, UK School of Chemistry, University of Leeds, Leeds LS2 9JT, UK CETEMPS – Dipartimento di Fisica, Università di L'Aquila, 67010 Coppito, L'Aquila, Italy Biogeochemistry Programme, Centre for Ecology and Hydrology, Penicuik, EH26 0QB, UK School of the Environment, University of Leeds, Leeds, LS2 9JT, UK National Center for Atmospheric Research, Boulder CO 80301, USA Department of Chemistry, University of York, York YO10 5DD, UK Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK Retired, formerly at Malaysian Meteorological Department, Jalan Sultan, Petaling Jaya, Selangor Darul Ehsan, Malaysia School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK Department of Chemistry, University of Edinburgh, Edinburgh EH9 3JW, UK now at: School of Engineering and Applied Sciences, Harvard University, MA, USA formerly at: School of Chemistry, University of Leeds, Leeds LS2 9JT, UK now at: Department of Chemistry, University of Reading, Reading RG6 6AH, UK deceased 12 01 2010 10 1 169 199 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/10/169/2010/acp-10-169-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/169/2010/acp-10-169-2010.pdf

In April–July 2008, intensive measurements were made of atmospheric composition and chemistry in Sabah, Malaysia, as part of the "Oxidant and particle photochemical processes above a South-East Asian tropical rainforest" (OP3) project. Fluxes and concentrations of trace gases and particles were made from and above the rainforest canopy at the Bukit Atur Global Atmosphere Watch station and at the nearby Sabahmas oil palm plantation, using both ground-based and airborne measurements. Here, the measurement and modelling strategies used, the characteristics of the sites and an overview of data obtained are described. Composition measurements show that the rainforest site was not significantly impacted by anthropogenic pollution, and this is confirmed by satellite retrievals of NO<sub>2</sub> and HCHO. The dominant modulators of atmospheric chemistry at the rainforest site were therefore emissions of BVOCs and soil emissions of reactive nitrogen oxides. At the observed BVOC:NO<sub>x</sub> volume mixing ratio (~100 pptv/pptv), current chemical models suggest that daytime maximum OH concentrations should be ca. 10<sup>5</sup> radicals cm<sup>&minus;3</sup>, but observed OH concentrations were an order of magnitude greater than this. We confirm, therefore, previous measurements that suggest that an unexplained source of OH must exist above tropical rainforest and we continue to interrogate the data to find explanations for this.

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