Methyl chloride and isoprene emissions from tropical rain forest in Southeast Asia

Methyl chloride (CH 3 Cl) fluxes were investigated at leaf and forest‐canopy scales in tropical forests in Malaysia. Screening of CH 3 Cl‐emitting species showed that 21% of 117 tree species were CH 3 Cl emitters; the percentage was markedly higher for dipterocarps (66%) than non‐dipterocarps (6%). The dipterocarp‐derived CH 3 Cl was characterized by high emissions (median: 0.03 μ g g −1 h −1 ) and low stable carbon isotope ratios (mean: −88.9 ± 11.0‰). Measurements of CH 3 Cl above the canopy showed a slight decrease in the mixing ratios with increasing height. These values were used to estimate the canopy‐scale flux of about 14 μ g m −2 h −1 , comparable to that extrapolated from the leaf‐scale emissions. Using the canopy‐scale flux, global CH 3 Cl emission by tropical forests was estimated to be 1.3 Tg yr −1 , representing approximately 30% of the global emissions. Above‐canopy measurements were also made for isoprene, with a mean flux of 1.2 mg m −2 h −1 .