Results from the International Halocarbons in Air Comparison Experiment (IHALACE)

Abstract

The International Halocarbons in Air Comparison Experiment (IHALACE) was conducted to document relationships between calibration scales among various laboratories that measure atmospheric greenhouse and ozone depleting gases. Six stainless steel cylinders containing natural and modified natural air samples were circulated among 19 laboratories. Results from this experiment reveal relatively good agreement among commonly used calibration scales for a number of trace gases present in the unpolluted atmosphere at pmol mol⁻¹ (parts per trillion) levels, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Some scale relationships were found to be consistent with those derived from bi-lateral experiments or from analysis of atmospheric data, while others revealed discrepancies. The transfer of calibration scales among laboratories was found to be problematic in many cases, meaning that measurements tied to a common scale may not, in fact, be compatible. These results reveal substantial improvements in calibration over previous comparisons. However there is room for improvement in communication and coordination of calibration activities with respect to the measurement of halogenated and related trace gases

U.S. emissions of HFC‐134a derived for 2008–2012 from an extensive flask‐air sampling network

“…The accuracy of this scale is estimated to be better than 2% based on consideration of impurities in the starting reagent material, and uncertainties in gravimetry and in the molecular mass of the diluent air. Intercomparison among laboratories that make the global measurements of HFC‐134a (e.g., Advanced Global Atmospheric Gases Experiment) suggests consistency within 2% with the NOAA results [ Hall et al ., ; Montzka et al ., ]. Consistency in calibration is ensured over time by repeated analyses of a suite of gravimetric standards and a suite of archived real air samples stored at high pressure in silanized aluminum or humidified electropolished stainless steel cylinders (for more measurement details, see Montzka et al .…”

Very short-lived bromomethanes measured by the CARIBIC observatory over the North Atlantic, Africa and Southeast Asia during 2009–2013

“…Mixing ratios in these standards are known to be stable over a period of years (e.g. Hall et al, 2013;Butler et al, 2007, supplemental). These comparisons are performed periodically and allow an assessment of any potential changes in the absolute mixing ratio of halocarbons in our working standard over time.…”

“…Laube et al, 2008;Hall et al, 2013;Butler et al, 2007, supplemental). Regular comparisons to known standards are necessary to ensure a consistent dataset.…”

“…Therefore, changes in chemistry in the UTLS may have consequences for tropospheric chemistry (Anderson et al, 2012) and climate (Riese et al, 2012). Additionally, it is possible that future climate change may impact on VSLB transport into the UTLS through changes in oceanic emissions as ocean temperature and acidity change and also through atmospheric processes such as increased convection and large-scale vertical transport (Dessens et al, 2009) or sea surface temperature, wind speed and marine boundary layer height (Hepach et al, 2014). These factors might increase the quantity of VSLB transported to the UTLS and hence, impact on stratospheric ozone.…”

Atmospheric histories and global emissions of halons H‐1211 (CBrClF2), H‐1301 (CBrF3), and H‐2402 (CBrF2CBrF2)

“…The comparisons are based on field observations from the colocated measurement sites Mace Head, Trinidad Head, Cape Matatula, and Cape Grim (AGAGE ADS/Medusa‐GCMS and NOAA flask results) for 1998–2015 for H‐1211 and 2004–2015 for H‐1301 and H‐2402. Based on these intercomparisons and also using the results from the laboratory intercomparison of the International Halocarbon in Air Comparison Experiment[ Hall et al , ], the average conversion factor from NOAA‐2006 to SIO‐05 for H‐1211 is 1.016 ± 0.007 (for the NOAA GCMS flask data only, this factor is 1.020 and for the CATS ECD data only, the factor is 1.008). For H‐1301, the NOAA‐to‐SIO conversion factor is 1.025 ± 0.011 (Table ) for both NOAA data sets.…”