Stable carbon isotope ratio of methyl chloride emitted from glasshouse‐grown tropical plants and its implication for the global methyl chloride budget

Stable carbon isotope ratios of methyl chloride (CH 3 Cl) were measured in foliar emissions from 14 species of tropical plants growing in a glasshouse. The isotopic ratio of CH 3 Cl (arithmetic mean: −83.2 ± 15.2‰) ranged from −56‰ to −114‰; that from dipterocarp trees (−87.4 ± 12.3‰) was on average more depleted in 13 C than that from tree ferns (−61.9 ± 9.7‰). The isotopic ratio was lower than that of CH 3 Cl produced by other known sources (e.g., biomass burning and salt marshes), with the exception of that by dead leaves. Using the distinctive isotope ratio of CH 3 Cl emitted from tropical plants together with previously reported isotopic data of CH 3 Cl sources and sinks to an isotopic mass balance calculation, global CH 3 Cl emission by tropical plants was estimated to be approximately 1500–3000 Gg yr −1 with uncertainties of 30–60%, which could account for 30–50% of the global emission.