Fluxes and concentrations of volatile organic compounds from a South-East Asian tropical rainforest

Abstract

Abstract. As part of the OP3 field study of rainforest atmospheric chemistry, above-canopy fluxes of isoprene, monoterpenes and oxygenated volatile organic compounds were made by virtual disjunct eddy covariance from a SouthEast Asian tropical rainforest in Malaysia. Approximately 500 hours of flux data were collected over 48 days in AprilMay and June-July 2008. Isoprene was the dominant nonmethane hydrocarbon emitted from the forest, accounting for 80% (as carbon) of the measured emission of reactive carbon fluxes. Total monoterpene emissions accounted for 18% of the measured reactive carbon flux. There was no evidence for nocturnal monoterpene emissions and during the day their flux rate was dependent on both light and temperature. The oxygenated compounds, including methanol, acetone and acetaldehyde, contributed less than 2% of the total measured reactive carbon flux. The sum of the VOC fluxes measured represents a 0.4% loss of daytime assimilated carbon by the canopy, but atmospheric chemistry box modelling suggests that most (90%) of this reactive carbon is returned back to the canopy by wet and dry deposition following chemical transformation. The emission rates of isoprene and monoterpenes, normalised to 30 • C and 1000 µmol m −2 s −1 PAR, were 1.6 mg m −2 h −1 and 0.46 mg m −2 h −1 respectively, which was 4 and 1.8 times lower respectively than the default value for tropical forests in the widely-used MEGAN Correspondence to: B. Langford (b.langford1@lancaster.ac.uk) model of biogenic VOC emissions. This highlights the need for more direct canopy-scale flux measurements of VOCs from the world's tropical forests.

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 all the stages relevant to these technologies are necessary and OP3 has provided some important new information on emissions and atmospheric chemistry. Flux measurements of isoprene, over both rainforest and oil palm plantations, and of NO x , have been made [4,17,18]. In addition, a range of in situ chemistry measurements has allowed the local chemical processes to be explored [5].…”

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

“…Identifying missing reactive carbon in the atmosphere can be informed to some extent by considering the "gaps" in capability left by existing instrumentation. The OP3 project used three instruments to determine reactive gas phase carbon: a GC-FID, a GC-MS and a PTR-MS Langford et al, 2010). This is typical of many largescale process studies.…”

Isoprene emissions from a tundra ecosystem

“…Most field studies of isoprene emissions have focused on temperate ecosystems (e.g., Goldstein et al, 1995;Pressley et al, 2005;McKinney et al, 2011) due to accessibility and tropical ecosystems (e.g., Geron et al, 2002;Rinne et al, 2002;Langford et al, 2010) because warm temperatures, high biomass densities, and long growing seasons drive globally significant fluxes. Other studies have stretched from savannahs (e.g., Guenther et al, 1996;Otter et al, 2003) to boreal forests (e.g., Rinne et al, 2000;Spirig et al, 2004).…”