Scientists tracking levels of greenhouse gases like methane and carbon dioxide need a primary reference standard to compare their measurements to, but at the moment the only available standards for these gases come from air samples collected at the top of Niwot Ridge mountain in Colorado, which are stored at the US National Oceanic and Atmospheric Administration (NOAA).
Demand for standards is rising as the number of atmospheric measurements taken around the world increases, so Paul Brewer and colleagues at the National Physical Laboratory have blended synthetic air identical in composition to the samples held by the NOAA in the lab. They used high accuracy gravimetry – essentially weighing the different gas components in the cylinder – to mix their standards, ensuring the correct isotopic composition of carbon dioxide by using a blend of carbon-12 and carbon-13 enriched carbon dioxide. The techniques they used can be applied elsewhere, so labs around the world need not rely on samples from remote locations.
P J Brewer et al, Anal. Chem., 2014, DOI: 10.1021/ac403982m