Screening of methyl chloride emitting plants in the sub-tropics and a study on the controlling factors of methyl chloride emission.

1 . Screening of methyl chloride emitting plantsIn order to find methyl chloride emitting plants我们put one or multiple leaves detached from a plant into a 40ml -vialmeasured methyl chloride concentration in it after a few days. Two hundred and fourteen speciessubtropical plants collected in Iriomote Island. Thirty-two species among them wund toemit methyl chloride with average emission rate of 0.11 ~ 0.51μg·(g drywt)^<-1> hr^<-1>.(2)Measurements of atmospheric methyl chloride in Iriomote IslandAir samples werecollected at 5 sites in August and at 6 sites in February，and were analyzed for methyl chloride. Highest concentration, 2750pptwas observed at a forestal site. In the samples collected at coastal sitesppt difference was found between the upwind sample and the downwind sample，suggesting accumulation of methyl chloride during the transport over the island covered by tropicalforests. Based on the wind velocity and assumed mixing heightthe emission rate of methyl chloride from the forest was calculated to be 5 ~ 100μg·m^<-2>·h^<-1>，which would correspond to annual total emission of 10 ~ 250 metric ton from the whole(3)Factors affecting methyl chloride emission from plantsFoliar emission rates of methylchloride from tropical tree ferns were investigated using a bag enclosure method. Cyateha lepifera一个midday decline in emission ratesCyathea podophyla showed a midday maximum. However，both of the ferns had a midday minimum in their methyl chloride emission in the experiment using adynamic mass balance chamber. Increased ambient temperature enhanced methyl chloride emission fromCyathea podophylla，但suppressed the emission from Cyateha lepifera。

(1)Screening of methyl chloride emitting plantsIn order to find methyl chloride emitting plants, we put one or multiple leaves detached from a plant into a 40 ml-vial, and measured methyl chloride concentration in it after a few days. Two hundred and fourteen species of subtropical plants were collected in Iriomote Island. Thirty-two species among them were found to emit methyl chloride with average emission rate of 0.11〜0.51μg・(g dry wt)^<-1>・hr^<-1>.(2)Measurements of atmospheric methyl chloride in Iriomote IslandAir samples were collected at 5 sites in August and at 6 sites in February, and were analyzed for methyl chloride. Highest concentration, 2750 ppt, was observed at a forestal site. In the samples collected at coastal sites, 40〜50 ppt difference was found between the upwind sample and the downwind sample, suggesting accumulation of methyl chloride during the transport over the island covered by tropical forests. Based on the wind velocity and assumed mixing height, the emission rate of methyl chloride from the forest was calculated to be 5〜100μg・m^<-2>・h^<-1>, which would correspond to annual total emission of 10〜250 metric ton from the whole island.(3)Factors affecting methyl chloride emission from plantsFoliar emission rates of methyl chloride from tropical tree ferns were investigated using a bag enclosure method. Cyateha lepifera showed a midday decline in emission rates, whereas Cyathea podophyla showed a midday maximum. However, both of the ferns had a midday minimum in their methyl chloride emission in the experiment using a dynamic mass balance chamber. Increased ambient temperature enhanced methyl chloride emission from Cyathea podophylla, but suppressed the emission from Cyateha lepifera.