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AGU: Journal of Geophysical Research, Atmospheres

 

Keywords

  • methane sinks
  • MBL chlorine
  • 13C in methane

Index Terms

  • Atmospheric Composition and Structure: Troposphere: composition and chemistry
  • Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry
  • Atmospheric Composition and Structure: Air/sea constituent fluxes
  • Atmospheric Composition and Structure: Constituent sources and sinks
  • Atmospheric Processes: Ocean/atmosphere interactions
Abstract
Cited By (12)
 

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D11306, 8 PP., 2005
doi:10.1029/2004JD005650

Interannual variation of 13C in tropospheric methane: Implications for a possible atomic chlorine sink in the marine boundary layer

W. Allan

National Institute of Water and Atmospheric Research, Wellington, New Zealand

D. C. Lowe

National Institute of Water and Atmospheric Research, Wellington, New Zealand

A. J. Gomez

National Institute of Water and Atmospheric Research, Wellington, New Zealand

H. Struthers

National Institute of Water and Atmospheric Research, Lauder, New Zealand

G. W. Brailsford

National Institute of Water and Atmospheric Research, Wellington, New Zealand

We present methane mixing ratio and δ13C time series measured at Baring Head, New Zealand, and Scott Base, Antarctica, over the years 1991–2003. These data demonstrate that the apparent kinetic isotope effect (KIE) of the methane atmospheric sink (derived from the amplitudes of the mixing ratio and δ13C seasonal cycles) is generally much larger than would be expected if the sink were the hydroxyl radical alone and has changed significantly during the observation period on a timescale of ∼3 years. We show using a global transport model that this technique for deriving the KIE should be quite accurate for a single atmospheric sink and that the change with time is unlikely to arise from El Niño–Southern Oscillation transport effects. We infer that a sink in addition to hydroxyl is required. A strong candidate for this extra sink is atomic chlorine in the marine boundary layer (MBL). We derive the amplitude of the chlorine concentration seasonal cycle that would fully account for the apparent KIE. This amplitude ranges from ∼104 atom cm−3 in 1994–1996 to about 3 × 103 atom cm−3 in 1998–2000. If the KIE is enhanced throughout the free troposphere, the seasonal mean concentrations of atomic chlorine required in the MBL would be about 3 × 104 atom cm−3 in 1994–1996 and ∼104 atom cm−3 in 1998–2000.

Received 30 November 2004; accepted 1 April 2005; published 7 June 2005.

Citation: Allan, W., D. C. Lowe, A. J. Gomez, H. Struthers, and G. W. Brailsford (2005), Interannual variation of 13C in tropospheric methane: Implications for a possible atomic chlorine sink in the marine boundary layer, J. Geophys. Res., 110, D11306, doi:10.1029/2004JD005650.

Cited By

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