HR: 0800h
AN: A51B-0042    [Abstracts]
TI: Evidence for Terrestrial Sources of Methyl Iodide
AU: * Varner, R K
EM: ruth.varner@unh.edu
AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Sive, B C
EM: bcs@gust.sr.unh.edu
AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Russo, R S
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Zhou, Y
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: White, M L
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Csakai, A
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Beckman, P
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Ambrose, J
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Wingenter, O W
A51B-0042 AF: New Mexico Institute of Mining and Technology, Department of Chemistry, Socorro, NM 87001 United States
AU: Mao, H
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AU: Talbot, R W
A51B-0042 AF: University of New Hampshire, Climate Change Research Center Institute for the Study of Earth, Oceans and Space , Durham, NH 03824 United States
AB: The major source of methyl iodide (MeI) to the atmosphere has been shown to be supersaturation of ocean surface waters through biological and/or photoproduction pathways. Minor contributions of MeI to the atmosphere are release by rice plants/paddies, salt marshes and fungi. To date, there has been no direct evidence of a significant terrestrial source of MeI. We present the first direct evidence of a significant plant and soil source of MeI. Canopy measurements of MeI were made in the loblolly pine plantation at Duke Forest, Chapel Hill, North Carolina during a three week field campaign from September 8 through 28, 2004. Approximately 700, 2-liter electropolished stainless steel canisters (University of California, Irvine) were filled hourly at both ambient CO₂ (Ring 1) and elevated CO₂ (Ring 2) of the FACTS-1 Research Facility. Canister samples were collected simultaneously in Rings 1 and 2 each hour for a total of 12 days from a 16 m inlet. Additionally on September 20 and 24, simultaneous samples from both 16 m and 20 m were collected in Rings 1 and 2 in order to determine the gradient of MeI. The measurements from the 16m height indicate a diurnal pattern of increasing MeI at night resulting from a decrease in boundary layer height coupled with a local source of MeI. Gradient fluxes were calculated using CO₂ gradients and eddy covariance data from the site. The flux data indicate a positive flux of MeI out of the canopy. A second field campaign at Duke Forest from June 1 through 12, 2005 where we used Teflon bag branch enclosures to measure the flux of MeI from branches of Pinus taeda (loblolly pine) and Liquidambar styraciflua (sweetgum) over two 48-hour periods. Ambient and post-branch samples were collected at both Rings 1 and 2 approximately every 2 hours for each plant species. Canister analysis revealed significantly different concentrations of MeI from ambient to post-branch enclosure. Fluxes calculated based on emission of MeI per leaf area of the branch indicate that these two species are sources of MeI to the atmosphere. In order to determine if a soil source or sink was present, 2 Teflon coated aluminum collars were placed in the soil at each of Rings 1 and 2. The Teflon coated aluminum chambers (headspace of 30L) were placed on the collars and four canister samples were taken approximately every 12 minutes. MeI mixing ratios increased in the chamber headspace over the sampling period in both Rings 1 and 2. These enclosure measurements reveal that the soil surface is also a significant source of MeI to the atmosphere. These measurements indicate that large terrestrial sources of MeI exist and could have a significant impact on our understanding of the global MeI budget.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0322 Constituent sources and sinks
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0486 Soils/pedology (1865)
DE: 0490 Trace gases
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005