Development of a Northern Continental Air Standard Reference Material

Abstract

The National Institute of Standards and Technology (NIST) recently began to develop standard mixtures of greenhouse gases as part of a broad program mandated by the 2009 United States Congress to support research in climate change. To this end, NIST developed suites of gravimetrically assigned primary standard mixtures (PSMs) comprising carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-natural air balance at ambient mole fraction levels. In parallel, the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, charged 30 aluminum gas cylinders with northern hemisphere air at Niwot Ridge, Colorado. These mixtures, which constitute NIST Standard Reference Material (SRM) 1720 Northern Continental Air, were certified by NIST for ambient mole fractions of CO2, CH4, and N2O relative to NIST PSMs. NOAA-assigned values are also provided as information in support of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) Program for CO2, CH4, and N2O, since NOAA serves as the WMO Central Calibration Laboratory (CCL) for CO2, CH4, and N2O. Relative expanded uncertainties at the 95% confidence interval are <±0.06% of the certified values for CO2 and N2O and <0.2% for CH4, which represents the smallest relative uncertainties specified to date for a gaseous SRM produced by NIST. Agreement between the NOAA (WMO/GAW) and NIST values based on their respective calibration standards suites is within 0.05%, 0.13%, and 0.06% for CO2, CH4, and N2O, respectively. This collaborative development effort also represents the first of its kind for a gaseous SRM developed by NIST.

What is novel about certified reference materials?

“…NIST has a long history of producing synthetic greenhouse gas mixture SRMs (CO 2 , CH 4 , and N 2 O) based on gravimetric preparation. Recently, Rhoderick et al [3,4] reported the first CRMs for whole natural air with values assigned for greenhouse gases, denoted as SRM 1720 Northern Hemisphere Air [3] and SRM 1721 Southern Oceanic Air [4]. These unique SRMs consist of batches of 30 cylinders of pristine ambient air collected at two remote locations: (1) Niwot Ridge (CO, USA) for SRM 1720 and Baring Head, New Zealand for SRM 1721.…”

“…These unique SRMs consist of batches of 30 cylinders of pristine ambient air collected at two remote locations: (1) Niwot Ridge (CO, USA) for SRM 1720 and Baring Head, New Zealand for SRM 1721. Rhoderick et al [3,4] described the process of assigning certified values to each individual cylinder based on calibrating the instrumentation using a suite of gravimetrically-prepared NIST primary reference gas mixtures. The nominal values for the three gases were nearly identical for CO 2 (388 μmol/mol) and N 2 O (323 μmol/mol) in both SRMs, and the value for CH 4 in SRM 1720 is 5.6% higher (1860 μmol/mol).…”

“…In SRM 972a only one of four levels contained nonendogenous metabolites, i.e., only addition of 3-epi-25(OH)D 3 . The low level and normal levels of 25(OH)D 3 were from donor pools that were screened to provide target levels, and the high level of 25(OH)D 2 was achieved through donors supplemented with vitamin D 2 .…”

“…The low level and normal levels of 25(OH)D 3 were from donor pools that were screened to provide target levels, and the high level of 25(OH)D 2 was achieved through donors supplemented with vitamin D 2 . Another significant improvement for SRM 972a was the use of only LC-MS/MS methods that separated the 25(OH)D 3 and 3-epi-25(OH)D 3 isomers to assign the certified values.…”

Recent advances in measurement techniques for atmospheric carbon monoxide and nitrous oxide observations

“…To take full profit of these observations, the uncertainty of these measurements must be minimised which implies consistent data series with traceability to common reference standards. Within the GAW Programme, Central Calibration Laboratories (CCLs) provide reference standards that are linked to internationally accepted calibration scales (Rhoderick et al, 2016;Rhoderick et al, 2018). In addition, World Calibration Centres (WCCs) evaluate GAW stations through independent assessments by on-10 site system-and performance audits (Buchmann et al, 2009).…”