HR: 0800h
AN: A51C-0785    [Abstracts]
TI: $^{18}$O-depleted CO emission from boreal forest fire in Alaska
AU: * Nakagawa, F
EM: fuminaka@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido University, N10 W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Tsunogai, U
EM: urumu@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido University, N10 W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Komatsu, D D
EM: damboo@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido University, N10 W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Kim, Y
EM: kimyw@iarc.uaf.edu
AF: International Arctic Research Center University of Alaska Fairbanks, 930 Koyukuk Dr., P.O. Box 757335 , Fairbanks, AK 99775-7335 United States
AU: Tanaka, N
EM: norit@iarc.uaf.edu
AF: International Arctic Research Center University of Alaska Fairbanks, 930 Koyukuk Dr., P.O. Box 757335 , Fairbanks, AK 99775-7335 United States
AB: We determined the stable carbon and oxygen isotopic compositions of carbon monoxide (CO), together with those of methane and carbon dioxide, in Alaskan wildfire plume, and compared the results with those obtained during combustion experiment in the laboratory. Alaskan wildfire plumes were sampled during June, 2004, when the extensive wildfires were observed near Fairbanks, Alaska. Gas samples were collected in pre-evacuated 500ml glass bottles. The stable carbon and oxygen isotopic compositions of the trace gases were determined by using continuous-flow isotope ratio mass spectrometry, together with their mixing ratios. The gas samples were enriched in CO, ranging from 3.7 to 190 ppmv. Both carbon and oxygen isotopic compositions of CO exhibit homogeneous values of about -28 permil VPDB and about +8 permil VSMOW, respectively. The oxygen isotopic compositions are depleted in $^{18}$O relative to those emitted from high temperature combustion processes such as automobile exhaust and flaming biomass burning (more than +20 permil). Similar $^{18}$O-depleted CO is also observed in Siberian biomass burning plume (Bergamaschi et al., 1998). In order to clarify the origin of the $^{18}$O-depleted CO in the wildfire plumes, laboratory biomass burning experiments were carried out using a furnace of 50cm in both diameter and height. About 1kg of spruce, which is major in Alaskan forests, was burned and smoke gas samples were collected into glass bottles at 30-seconds to 3-minutes intervals. The results of the biomass burning experiment show that the stable carbon and oxygen isotopic compositions of CO and methane vary widely (about 20 permil) depending on their burning stages. During the flaming stage, CO and methane are enriched in $^{13}$C relative to carbon isotopic composition of fuel, whereas those are depleted in $^{13}$C during the smoldering stage. Similar trend was also found in the oxygen isotopic composition of CO. These variations in isotopic compositions are likely to be due to kinetic isotopic effects during both production processes and consumption processes (reaction with OH radical) of these gases. Based on these results, we conclude that most of carbon monoxide is emitted during the smoldering stage in the Alaskan forest fire. Besides, CO from boreal forest fire in general seems to be characterized by such $^{18}$O-depleted values of around +8 to +10 permil in atmospheric CO.
DE: 1704 Atmospheric sciences
DE: 1040 Isotopic composition/chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting