Seasonal changes of CO₂, CH₄, N₂O, and SF₆ in the upper troposphere/lower stratosphere over the Eurasian continent observed by commercial airliner

The seasonal variations of greenhouse gases at about 11km altitude were analyzed from monthly air samples collected aboard a commercial airliner flying between Europe and Japan from April 2012 to March 2014. Compared to lower latitudes, the upper troposphere between 50 and 70°N showed higher CH₄ and SF₆ and an earlier seasonal phase of CO_2. However, N₂O values were similar to those in the subtropics. CH₄, N₂O, and SF₆ in the lower stratosphere with potential temperature of up to 50K above the tropopause showed seasonal variations with maxima in November/December and minima in April/May. At potential temperatures of 37.5-50K above the tropopause, SF₆ age was estimated to be about 22months in May and 9months in November. This strong seasonal variation is explained by the subsidence of high-stratospheric air in spring and the effective flushing of the lowermost stratospheric air with tropospheric air in autumn. Key Points Higher CH₄, SF₆ at high latitudes in upper troposphere compared to subtropics Larger seasonal CO₂ changes at the high latitudes in the upper troposphere Clear SF₆ maximum in autumn in LS from tropospheric influences