HR: 0800h
AN: A21A-0838    [Abstracts]
TI: Measurements of mixing ratio and carbon-13 composition of atmospheric methyl chloride from two Atlantic Ocean transects
AU: * Rice, A L
EM: arice@ocean.washington.edu
AF: Department of Physics, Portland State University, PO Box 751, Portland, OR 97207 United States
AU: * Rice, A L
EM: arice@ocean.washington.edu
AF: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, 4909 25th Ave NE, Seattle, WA 98195 United States
AU: Huset, R
EM: rcesario@u.washington.edu
AF: Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195 United States
AU: Gammon, R
EM: gammon@u.washington.edu
AF: Program on the Environment, University of Washington, 274 Mary Gates Hall, Box 352802, Seattle, WA 98195 United States
AU: Bullister, J L
EM: John.L.Bullister@noaa.gov
AF: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AB: Measurements of methyl chloride (CH₃Cl) mixing ratio and ¹³C/¹²C isotope ratio were made on samples collected during two sections of the repeat hydrography surveys as part of the US Climate Variability and Predictability (CLIVAR) and Carbon Cycle Science Program (CCSP). The northern section, A16N, was operated between Reykjavik, Iceland (63° 17'N, 29° 0'W) and Natal, Brazil (6° 1'N, 20° 0'W) in June and August 2003. The southern section between Punta Arenas, Chile (52° 45'S, 70° 30'W ) and Fortaleza, Brazil (3° 42'S, 38° 31'W), A16S, took place during January and February of 2005. 47 whole air samples were collected through a bow line into 2.5-L electropolished stainless steel canisters and pressurized to several atmospheres using a Teflon diaphragm pump. All samples were measured for CH₃Cl mixing ratio using a gas chromatograph electron capture detector (GC-ECD) analytical system to a precision of 1%. The mean value for CH₃Cl mixing ratio measured was 551±38pptv. The meridional distribution of CH₃Cl shows higher than average values in the tropical mid-Atlantic (580pptv), with lower values in the extratropical southern hemisphere (520pptv) and roughly average values in the extratropical northern hemisphere (550pptv). The CH₃Cl maximum observed in the tropics is consistent with previous observational datasets. A subset of 22 samples from the dataset were measured by continuous-flow GC-isotope ratio mass spectrometry (GC-IRMS) for δ¹³C-CH₃Cl to a precision of 1‰. The mean measured value of -39.9±1.3‰ (versus VPDB) is somewhat depleted (2-4‰) compared with values reported in recent datasets. However, this new dataset presents significantly larger spatial coverage than previously reported. Spatial variability observed in δ¹³C-CH₃Cl suggest that isotopic CH₃Cl may be particularly useful in characterizing and constraining sources of atmospheric CH₃Cl. The tropical region, in particular is depleted by 1-2‰ relative to the extratropical northern hemisphere, mirroring the maximum in mixing ratio observed. Together with recent studies of δ¹³C isotopic signatures from CH₃Cl sources, these data support the prevalence of a depleted biogenic CH₃Cl source in tropical regions.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0490 Trace gases
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005