title: Development of a southern oceanic air standard reference material.
abstract: In 2009, the United States Congress charged the National Institute of Standards and Technology (NIST) with supporting climate change research. As part of this effort, the Gas Sensing Metrology Group at NIST began developing new gas standard mixtures for greenhouse gas mixtures relevant to atmospheric measurements. Suites of gravimetrically prepared primary standard mixtures (PSMs) were prepared at ambient concentration levels for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-air balance. In parallel, 30 gas cylinders were filled, by the National Institute of Water and Atmospheric Research (NIWA) in Wellington, New Zealand, to high pressure from pristine southern oceanic air at Baring Head, New Zealand, and shipped to NIST. Using spectroscopic instrumentation, NIST analyzed the 30 cylinder samples for mole fractions of CO2, CH4, and N2O. Certified values were assigned to these mixtures by calibrating the instrumentation with the PSM suites that were recently developed at NIST. These mixtures became NIST Standard Reference Material (SRM) 1721 Southern Oceanic Air and are certified for ambient mole fraction, the first of their kind for NIST. The relative expanded uncertainties corresponding to coverage intervals with 95% probability are no larger than 0.06% of the certified values, representing the smallest uncertainties to date ever assigned to an NIST gas SRM.
authors.affiliation: Gas Sensing Metrology Group, Chemical Sciences Division, Materials Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899-8393, USA. george.rhoderick@nist.gov.
authors.forename: George C
authors.initials: GC
authors.lastname: Rhoderick
authors.affiliation: Gas Sensing Metrology Group, Chemical Sciences Division, Materials Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899-8393, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Kelley
authors.affiliation: Gas Sensing Metrology Group, Chemical Sciences Division, Materials Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899-8393, USA.
authors.forename: Walter R
authors.initials: WR
authors.lastname: Miller
authors.affiliation: Tropospheric Chemistry, National Institute of Water and Atmospheric Research, Wellington, 6021, New Zealand.
authors.forename: Gordon
authors.initials: G
authors.lastname: Brailsford
authors.affiliation: Statistical Engineering Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899-8980, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Possolo
keywords: Gravimetric preparation; Long-lived greenhouse gases (LLGHG); Primary standard mixture (PSM); Southern oceanic air; Standard Reference Material (SRM)