Abstract
Abstract. Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.).
Highlights
Sulfur hexafluoride (SF6) is a potent greenhouse gas with a global warming potential (100 yr time horizon) 22 800 times that of carbon dioxide (Forster et al, 2007)
Measurements of atmospheric SF6 obtained by a number of researchers around the world are used to examine trends in SF6 emissions (Levin et al, 2010; Rigby et al, 2010), evaluate atmospheric transport models (Levin and Hesshaimer, 1996; Gloor et al, 2007; Patra et al, 2009), and for the study of stratospheric circulation and the calculation of air mass mean age (Park et al, 1999, Engel et al, 2008, Ray et al, 2010)
While laser-based N2O instruments are emerging, gas chromatography with electron capture detection is commonly used for SF6,and gas chromatographic methods with electron capture detection (GC-electron capture detector (ECD)) systems measuring both N2O and SF6 will likely be used for the foreseeable future
Summary
Measurements of atmospheric SF6 obtained by a number of researchers around the world are used to examine trends in SF6 emissions (Levin et al, 2010; Rigby et al, 2010), evaluate atmospheric transport models (Levin and Hesshaimer, 1996; Gloor et al, 2007; Patra et al, 2009), and for the study of stratospheric circulation and the calculation of air mass mean age (Park et al, 1999, Engel et al, 2008, Ray et al, 2010). The predominant method of SF6 measurement involves gas chromatography with detection by electron capture detector (ECD) or mass selective detector (MSD). Hall et al.: Improving measurements of SF6 for the study of atmospheric transport and emissions (Wanninkhof, 1991; Miller et al, 2008), the ECD is sufficiently sensitive to SF6 that pre-concentration is generally not required. We first describe a Porapak-Q-based system similar to that used to measure SF6 in NOAA/ESRL flask samples of ambient air since 1995 (Geller et al, 1997). We describe how this method was modified to improve SF6 precision on a laboratory-based GC used for calibration, and on one in situ system. While laser-based N2O instruments are emerging, gas chromatography with electron capture detection is commonly used for SF6,and GC-ECD systems measuring both N2O and SF6 will likely be used for the foreseeable future
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