Hewitt, C. N. and Lee, J. D. and Mackenzie, Rob and Barkley, M. P. and Carslaw, N. and Carver, G. D. and Chappell, Nicholas and Coe, H. and Collier, C. and Commane, R. and Davies, F. and Davison, Brian and Di Carlo, P. and Di Marco, C. F. and Dorsey, J. R. and Edwards, P. M. and Evans, M. J. and Fowler, D. and Furneaux, K. L. and Gallagher, M. and Guenther, A. and Heard, D. E. and Helfter, C. and Hopkins, J. and Ingham, T. and Irwin, M. and Jones, C. and Karunaharan, A. and Langford, Ben and Lewis, A. C. and Lim, S. F. and MacDonald, S. M. and Mahajan, A. S. and Malpass, S. and McFiggans, G. and Mills, G. and Misztal, P. and Moller, S. and Monks, P. S. and Nemitz, E. and Nicolas-Perea, V. and Oetjen, H. and Oram, D. E. and Palmer, P. I. and Phillips, G. J. and Pike, R. and Plane, J. M. C. and Pugh, Thomas and Pyle, J. A. and Reeves, C. E. and Robinson, N. H. and Stewart, D. and Stone, D. and Whalley, L. K. and Yin, X. (2010) Overview: oxidant and particle photochemical processes above a south-east Asian tropical rainforest (the OP3 project) : introduction, rationale, location characteristics and tools. Atmospheric Chemistry and Physics, 10 (1). pp. 169-199. ISSN 1680-7316
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Abstract
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 NO2 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:NOx volume mixing ratio (similar to 100 pptv/pptv), current chemical models suggest that daytime maximum OH concentrations should be ca. 10(5) radicals cm(-3), 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.