Constraining the atmospheric hydrogen oxidation and soil sink seasonal cycles 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 yr−1 is found, peaking in July–August, while the OH loss seasonal range is 8±1 Tg yr−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 yr−1, peaking in January–March. The OH loss in the South has a seasonal range of 7±1 Tg yr−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.