An examination of the total hydrogen budget of the lower stratosphere

We analyze the hydrogen budget of the lower stratosphere using simultaneous in situ measurements of northern hemispheric water vapor (H 2 O) and methane (CH 4 ) obtained during the spring Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE), as well as previously published in situ H 2 data. Based on this data, we conclude that approximately two H 2 O molecules are produced for each CH 4 molecule destroyed. This implies that H 2 production from CH 4 oxidation is balanced by H 2 oxidation. The uncertainty in this analysis is greatly reduced by the use of multiple data sets. Additionally, we infer that, on an annual and global average, H 2 O enters the stratosphere with a mixing ratio of 4.2±0.5 ppmv, and that the quasi‐conserved quantity 2×[CH 4 ] + [H 2 O] has a value of 7.6±0.6 ppmv in these northern hemisphere air parcels (where [ξ] denotes the mixing ratio of the constituent ξ).