Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements

Abstract

Hydrogen (H2), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts. The magnitudes and seasonal cycles of the major (presumably microbial) soil sink of hydrogen have been estimated from high‐frequency in situ AGAGE H2 observations and also from more geographically extensive but low‐frequency flask measurements from CSIRO and NOAA‐GMD using the Kalman filter in a two‐dimensional (2‐D) global transport model. Hydrogen mole fractions exhibit well‐defined seasonal cycles in each hemisphere with their phase difference being only about 3 months. The global production rate of H2 is estimated to be 103 ± 10 Tg yr−1 with only a small estimated interannual variation. Soil uptake (84 ± 8 Tg yr−1) represents the major loss process for H2 and accounts for 81% of the total destruction. Strong seasonal cycles are deduced for the soil uptake of H2. The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere. Oxidation by tropospheric OH (18 ± 3 Tg yr−1) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere. The calculated global burden is 191 ± 29 Tg, indicating an overall atmospheric lifetime of 1.8 ± 0.3 years. Hydrogen in the troposphere (149 ± 23 Tg burden) has a lifetime of 1.4 ± 0.2 years.

A new estimation of the recent tropospheric molecular hydrogen budget using atmospheric observations and variational inversion

“…For Bousquet et al (2011), we have indicated the standard deviation of the sensitivity inversions based on the reference scenario (external errors). The errors in Xiao et al (2007) include model uncertainties, absolute calibration error and errors in the assumed fossil fuel source strength. For each region, we indicate the relative proportion of each regional source or sink in comparison with the global source or sink.…”

“…The global estimations for each term as given in Xiao et al (2007) and Bousquet et al (2011) are added in Table 4. Estimating the uncertainties of the posterior fluxes can be done using the MonteCarlo approach of Chevallier et al (2007).…”

“…In contrast to CH 4 and other trace gases sharing anthropogenic sources, the observed H 2 mixing ratios are lower in the Northern Hemisphere when compared to the Southern Hemisphere due to the distribution of the sources and sinks of H 2 (Novelli et al, 1999). The strength of each term of the H 2 budget is given hereafter as referred to in the literature (Novelli et al, 1999;Hauglustaine and Ehhalt, 2002;Sanderson et al, 2003;Rhee et al, 2006;Xiao et al, 2007;Price et al, 2007;Ehhalt and Rohrer, 2009) and compiled in Ehhalt and Rohrer (2009). The main sources of H 2 are photochemical production by the transformation of formaldehyde (HCHO) in the atmosphere and incomplete combustion processes.…”

“…Atmospheric inversions have already been developed to study H 2 , but the studies remain sparse: Xiao et al (2007) have used a 2D latitude-vertical 12 box model for atmospheric chemistry in an inversion framework combined with AGAGE, NOAA and CSIRO measurements to estimate the magnitude and variability of H 2 sources and sinks for four semi-hemispheres over the 1993-2004 period. Pison et al (2009) presented a first inversion of H 2 using the same simplified chemistry scheme and model as in this study.…”

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

“…The two major atmospheric H 2 sources are photochemical production from methane and non-methane hydrocarbons and combustion of fossil fuels and biomass (Novelli et al, 1999). The major H 2 sinks are soil consumption, representing about 81 ± 8 % of the total sink, and oxidation by OH being about 17 ± 3 % based on a global inversion of sparse atmospheric H 2 measurements (Xiao et al, 2007). The major sources and sinks are nearly balanced so atmospheric H 2 concentrations are stable.…”