Developing tracer interrelationships to derive stratospheric age of air from satellite observations of nitrous oxide

Chemistry-climate models predict a strengthening of the Brewer-Dobson Circulation (BDC) in response to climate change, which has implications for global atmospheric composition, radiation, and climate. This predicted acceleration has not been confirmed with observations, and models also disagree about the mean stratospheric circulation and mixing strength. The BDC impacts the distribution of long-lived tracers and their empirical relationships with one another. Age of air is an important diagnostic for changes in the BDC, and it can be derived from long-lived trace gases, such as sulfur hexafluoride (SF₆) and nitrous oxide (N₂O). We introduce an updated technique to calculate age of air using satellite observations of N₂O. We (1) compute tracer interrelationships of age of air and N₂O (Age:N₂O) and demonstrate that they vary with latitude, and then (2) use these relationships to calculate a new N₂O-derived age timeseries that takes this latitude variability into account from 2005 to 2012. The tracer interrelationships and their variability with latitude provide a better understanding of the structure and seasonality of the BDC. In particular, latitudinally-resolved Age:N₂O relationships reflect the relative importance of photochemical loss of N₂O in different regions and enable hemispheric structural comparisons. The N₂O-age product has more extensive spatial coverage than previous counterparts. Additionally, N₂O and SF₆-age compare well, showing that Age:N₂O relationships are robust on seasonal and interannual time scales. While this timeseries is only 7 years long, this manuscript lays the groundwork for calculating a longer record of N₂O-age to understand long-term variability and shifts of the BDC.