Evaluation of Stratospheric Age of Air Estimated from Halocarbon Measurements of Air Samples Collected by a Balloon-Borne Cryogenic Air Sampler over Japan

To diagnose stratospheric transport, the mean age of air, the transit time of an air parcel from the troposphere to the stratosphere, has been estimated from measurements of trace gases, typically CO2 and SF6. Here we present a new set of halocarbon measurements on air samples collected at 15-35 km above Japan in 2020 using a balloon-borne cryogenic sampler. The mean ages of air were estimated based on a variety of trace gases combined with reference time series at the surface. The mean ages of air from HFC-23 and HFC-227ea showed general agreement to those derived from CO2 and SF6, which varied from < 2 yr below 20 km to almost constant values of ∼5 yr above ∼25 km altitude. In addition to conservation of the tracer in the stratosphere, measurement precision was found to be decisive to precisely estimate the mean age of air. We examined the age of air estimated from multiple tracers for future investigation towards improving assessment of the long-term trend in stratospheric circulation.