Overview: oxidant and particle photochemical processes above a south-east Asian tropical rainforest (the OP3 project): introduction, rationale, location characteristics and tools

Abstract

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 rainforCorrespondence to: C. N. Hewitt (n.hewitt@lancaster.ac.uk) est" (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 Published by Copernicus Publications on behalf of the European Geosciences Union. 170 C. N. Hewitt et al.: The OP3 project: introduction, rationale, location characteristics and tools site was not significantly impacted by anthropogenic pollution, and this is confirmed by satellite retrievals of NO 2 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 x volume mixing ratio (∼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.

The impact of local surface changes in Borneo on atmospheric composition at wider spatial scales: coastal processes, land-use change and air quality

“…Analysis of a 12 year time series of monthly mean HCHO columns retrieved from the GOME and SCIA-MACHY satellite instruments [25,26] and ATSR/ AATSR fire-counts [24,27] confirm that biomass burning over Borneo drives observed variability of HCHO [3]. Anomalously high HCHO columns over this period were owing to intense burning periods associated with strong El Niñ o conditions, as expected.…”

“…In Malaysia, 13 per cent of land is now covered by oil palm plantations, compared with 1 per cent less than 40 years ago [3]. Production for the global food industry has been one of the major drivers.…”

“…(b) Model comparison with measurements During OP3, a range of atmospheric composition measurements was made in the Danum Valley and from the FAAM BAe146 research aircraft, which made a series of survey flights of Sabah, including low-level flights over Danum [3,5]. These measurements allow local chemical and physical processes to be investigated and their treatments in atmospheric models to be evaluated.…”

“…Hewitt et al [2,3] provide a detailed description of the campaign objectives and various approaches and techniques adopted. Ground-based measurements at the Bukit Atur Global Atmosphere Watch station in the Danum Valley forest conservation area in Sabah, Malaysia (4858 0 N, 117850 0 E, 426 m above mean sea level) and at the Sabahmas oil palm plantation, also in Sabah (584 0 N, 118827 0 E), owned by Wilmar International Ltd., were complemented by airborne measurements made using the FAAM BAe146 research aircraft.…”

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

“…The maximum contributions of HO 2 (as measured by FAGE) to the hourly-averaged daytime budget of total peroxy radicals (as measured by PERCA) were 40 %, 45 % and 34 % for SOS 1, 2 and 3, respectively. Measurements in the Borneo rainforest in 2009 in the OP3 campaign (Hewitt et al, 2010) gave HO 2 /HO 2 + RO 2 an average ratio of 15 % for day light hours (Arunasalam personal communication), similar to the approximate 10 % daily maximum ratios during the OOMPH Southern Ocean cruise (Hosaynali Beygi et al, 2011) but daylight ratios at Mace Head, Ireland were between 10 and 40 % on low NO x days and up to 70 % on high NO x days in summer 2002 (Fleming et al, 2006).…”