17 Jul 2023
 | 17 Jul 2023

Reanalysis of NOAA H2 observations: implications for the H2 budget

Fabien Paulot, Gabrielle Pétron, Andrew M. Crotwell, and Matteo B. Bertagni

Abstract. Hydrogen (H2) is being considered for many applications as an alternative to fossil fuels. Robust assessment of the climate implications of increased H2 usage in the global economy is partly hindered by uncertainties in its biogeochemical cycle. Here we use NOAA H2 dry air mole fraction observations from air samples collected from ground-based and ship platforms from 2010 to 2019 to evaluate the representation of H2 in the NOAA GFDL-AM4.1 atmospheric chemistry-climate model. We find that the model captures the observed interhemispheric gradient well but underestimates the surface concentration of H2 by about 10 ppbv. Observations show a 1–2 ppbv/year mean increase in surface H2 at background stations, while the simulated H2 exhibits no significant change over the 2010–2019 period. We show that this model bias is primarily driven by the estimated decrease of anthropogenic emissions, mostly from transportation, and that including leakage from H2-producing facilities can improve the simulated trend. We find that changes in soil moisture, soil temperature, and snow cover likely increase the magnitude and modify spatial distribution of the soil sink, the most important removal mechanism for atmospheric H2. However, the magnitude and even the sign of such changes is uncertain due to fundamental gaps in our understanding of H2 soil removal, such as the minimum soil moisture for H2 soil uptake. We show that the observed meridional gradient of H2 mixing ratio and its seasonality provide important constraints to test and refine parameterizations of H2 soil removal.

Fabien Paulot et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1602', Anonymous Referee #1, 16 Sep 2023
  • RC2: 'Comment on egusphere-2023-1602', Anonymous Referee #2, 12 Nov 2023

Fabien Paulot et al.

Fabien Paulot et al.


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Short summary
New observations from NOAA show that H2 concentration has increased from 2010 to 2019. This is consistent with the simulated increase in H2 photochemical production (primarily from methane). However, it cannot be reconciled with the expected decrease (increase) of H2 anthropogenic emissions (soil deposition) over the same time period. This highlights gaps in our understanding of the H2 biogeochemical cycle that need to be resolved to quantify the impact of the higher H2 usage.