Improving the in situ observation-based long-term record of stratospheric age of air 

Stratospheric mean age of air is an important metric and much-used proxy for the speed of the residual overturning circulation in the stratosphere. Much effort has been put into better constraining observation-based estimates of age of air over the past two decades. Yet substantial uncertainties remain for some aspects such as the long-term evolution, especially at higher altitudes that are hard to reach for most in situ-measurement platforms. We here present a newly derived age of air data set, which is based on high precision measurements of inert trace gases that were derived from a) AirCore samples from multiple weather balloon-based deployments since 2017 (updated from Laube et al., 2020), and also b) recently collected as well as archived reanalysed air samples from high altitude aircraft and large balloon campaigns between 1976 and 2017. Utilised trace gases include SF6, C2F6, C3F8, CHF3 (HFC-23), and C2HF5 (HFC-125), all of which have been proven to be suitable as age tracers (Leedham Elvidge et al., 2018). We evaluate the uncertainties connected to the trace gas measurements as well as the derivation of the mean age of air, and compare our estimates to published data sets such as the one from Engel et al. (2017).   References Engel, et al., Atmos. Chem. Phys., 2017, https://doi.org/10.5194/acp-17-6825-2017. Laube et al., Atmos. Chem. Phys., 2020, https://doi.org/10.5194/acp-20-9771-2020. Leedham Elvidge et al., Atmos. Chem. Phys., 2018, https://doi.org/10.5194/acp-18-3369-2018.