Identification and quantification of methyl halide sources in a lowland tropical rainforest

In conjunction with the OP3 campaign in Danum Valley, Malaysian Borneo, flux measurements of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were performed from both tropical plant branches and leaf litter in June and July 2008. Live plants were mainly from the Dipterocarpaceae family whilst leaf litter samples were representative mixtures of different plant species. Environmental parameters, including photosynthetically-active radiation, total solar radiation and air temperature, were also recorded. The dominant factor determining magnitude of methyl halide fluxes from living plants was plant species, with specimens of the genus Shorea showing persistent high emissions of both gases, e.g. Shorea pilosa: 65 ± 17 ng CH3Cl h−1 g−1 (dry weight foliage) and 2.7 ± 0.6 ng CH3Br h−1 g−1 (dry weight foliage). Mean CH3Cl and CH3Br emissions across 18 species of plant were 19 (range, <LOD −76) and 0.4 (<LOD −2.9) ng h−1 g−1 respectively; fluxes from leaf litter were 1–2 orders of magnitude smaller per dry mass. CH3Cl and CH3Br fluxes were weakly correlated. Overall, the findings suggest that tropical rainforests make an important contribution to global terrestrial emissions of CH3Cl, but less so for CH3Br.