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Press Releases Land can emit methyl iodide too environmentalresearchweb November 14, 2007 DURHAM - To date, scientists believed that the only important source of atmospheric methyl iodide (CH3I) was the oceans, with rice fields, salt marshes and fungi playing a much lesser role. But now a team from the US has found that vegetation and soils can emit the chemical in comparable amounts to the oceans. “Methyl iodide is the most abundant organoiodine compound in the atmosphere and it can influence ozone chemistry, aerosol formation, and ultimately the atmosphere’s oxidizing capacity,” Barkley Sive of the University of New Hampshire told environmentalresearchweb. “We have identified significant terrestrial sources of methyl iodide.” Sive and colleagues at the University of California, Irvine and New Mexico Tech found that the terrestrial methyl iodide flux was around 2,700 ng/m2/day at Thompson Farm in Durham, New Hampshire and 1,800 ng/m2/day at Duke Forest in North Carolina. For comparison, current estimates of the ocean emission flux of methyl iodide are ˜2,600 ng/m2/day. “This suggests that the terrestrial and oceanic fluxes are comparable in magnitude, which accounts for the similarity in the vertical profiles of methyl iodide we observed in both the marine and terrestrial environments,” said Sive. The team took their measurements using a combination of aircraft sampling over the US and North Atlantic, the AIRMAP ground-observing network in New England, and a field campaign in a mid-latitude forest. They used a combination of canister samples that were later analysed by gas chromatography and in situ measurements. Methyl iodide levels tended to be higher from late March to mid-October, tieing in with the growing season in New England. The researchers estimate that vegetation was the dominant source of terrestrial methyl iodide, providing roughly 900 ng/sq.m/day, with soils contributing 500 ng/m2/day. According to the scientists, on a global basis, the average terrestrial flux of ˜2,300 ng/m2/day over an active season of 240 days together with biome areas as calculated by Guenther et al. 1995 for temperate forest and woodlands (28.5 × 1012 m2) and temperate grasslands (31.9 × 1012 m2), yield a source strength of 33 Gg/year for methyl iodide. “Measurements are needed in tropical and boreal areas to improve and expand upon our terrestrial flux estimates and facilitate development of a more accurate global budget,” said Sive. “Ultimately, we plan to continue characterizing the terrestrial methyl iodide sources by carrying out additional field campaigns.” The researchers reported their work in Geophysical Research Letters. Citation Kalaugher, Liz (2007, November 7). Land can emit methyl iodide too. environmentalresearchweb, Retrieved January 22, 2008, from http://environmentalresearchweb.org/cws/article/research/31793. |
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