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Strong emission of methyl chloride from tropical plants


Methyl chloride is the largest natural source of ozone-depleting chlorine compounds, and accounts for about 15 per cent of the present atmospheric chlorine content1. This contribution was likely to have been relatively greater in pre-industrial times2, when additional anthropogenic sources—such as chlorofluorocarbons—were absent. Although it has been shown that there are large emissions of methyl chloride from coastal lands in the tropics3,4, there remains a substantial shortfall in the overall methyl chloride budget. Here we present observations of large emissions of methyl chloride from some common tropical plants (certain types of ferns and Dipterocarpaceae), ranging from 0.1 to 3.7 µg per gram of dry leaf per hour. On the basis of these preliminary measurements, the methyl chloride flux from Dipterocarpaceae in southeast Asia alone is estimated at 0.91 Tg yr-1, which could explain a large portion of missing methyl chloride sources. With continuing tropical deforestation, natural sources of chlorine compounds may accordingly decrease in the future. Conversely, the abundance of massive ferns in the Carboniferous period5 may have created an atmosphere rich in methyl chloride.

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Figure 1: Atmospheric concentrations of CH3Cl and COS during the observation periods, 5–8 September and 17–20 October.


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We thank T. Konishi for permission to use the Rainforest Glasshouse, Tsukuba Botanical Garden; S. Yamauchi for permission to use Yanbaru Subtropical Forest Park; P. Ciccioli for suggestions on the measurements of flux; T. Okuda, A. Takenaka, K. Kitayama and T. Ueda for comments and discussion; and T. Enomoto for help with sampling.

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Correspondence to Yoko Yokouchi.

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Yokouchi, Y., Ikeda, M., Inuzuka, Y. et al. Strong emission of methyl chloride from tropical plants. Nature 416, 163–165 (2002).

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