Constraining the atmospheric hydrogen oxidation and soil sinks using HFC-152a

Abstract. As the hydrogen (H₂) economy expands, there is growing interest in understanding the atmospheric lifetime of H₂, which affects its impact on atmospheric chemistry and climate. While some global H₂ is destroyed via reaction with the hydroxyl radical (OH), most is lost to microbial activity in soils. However, the sources and sinks of H₂ are still uncertain on global and local scales. This study focuses on how monthly resolved observations of HFC-152a can help to constrain the seasonal OH cycle and the H₂ budget, particularly the seasonal range and phase of H₂ oxidation and soil loss. Seasonal observations of HFC-152a are used to constrain OH through a Bayesian inversion in a three-box model comprising the Northern, Tropics, and Southern regions over 2010–2022. In the North, a seasonal range of the soil sink of 18–21 ± 8 Tg year^-1 is found, peaking in July–August, while the OH loss seasonal range is 8 ± 1 Tg year^-1, peaking in July. The South has much less land and so displays a smaller soil sink seasonal range of 2–3 ± 2.5 Tg year^-1, peaking in January–March. The OH loss in the South has a seasonal range of 7 ± 1 Tg year^-1, peaking in January. The OH and soil sink loss in the Tropics is more consistent across all months, but with larger uncertainty. The results presented here will be a useful comparison for H₂ cycles in fully integrated chemistry climate models.