Temporal and spatial variability of the stable isotopic composition of atmospheric molecular hydrogen: observations at six EUROHYDROS stations

Abstract

Abstract. Despite the potential of isotope measurements to improve our understanding of the global atmospheric molecular hydrogen (H 2 ) cycle, few H 2 isotope data have been published so far. Now, within the EUROpean network for atmospheric HYDRogen Observations and Studies project (EU-ROHYDROS), weekly to monthly air samples from six locations in a global sampling network have been analysed for H 2 mixing ratio (m(H 2 )) and the stable isotopic composition of the H 2 (δ(D,H 2 ), hereafter referred to as δD). The time series thus obtained now cover one to five years for all stations. This is the largest set of ground station observations of δD so far. Annual average δD values are higher at the Southern Hemisphere (SH) than at the Northern Hemisphere (NH) stations; the maximum is observed at Neumayer (Antarctica), and the minimum at the non-arctic NH stations. The maximum seasonal differences in δD range from ≈18 ‰ at Neumayer to ≈45 ‰ at Schauinsland (Southern Germany); in general, seasonal variability is largest at the NH stations. The timing of minima and maxima differs per station as well. In Alert (Arctic Canada), the variations in δD and m(H 2 ) can be approximated as simple harmonic functions with a ≈5-month relative phase shift. This out-of-phase seasonal behaviour of δD and m(H 2 ) can also be detected, but delayed and with a ≈6-month relative phase shift, at Mace Head and Cape Verde. However, no seasonal δD cycle could be observed at Schauinsland, which likely reflects the larger influence of local sources and sinks at this continental station.Correspondence to: A. M. Batenburg (a.m.batenburg@uu.nl) At the two SH stations, no seasonal cycle could be detected in the δD data. If it is assumed that the sink processes are the main drivers of the observed seasonality in m(H 2 ) and δD on the NH, the relative seasonal variations can be used to estimate the relative sink strength of the two major sinks, deposition to soils and atmospheric oxidation by the hydroxyl (OH) radical. For the NH coastal and marine stations this analysis suggests that the relative contribution of soil uptake to the total annual H 2 removal increases with latitude.

The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft

“…Recently, isotope effects in the production processes of H 2 have been studied (Gerst and Quay, 2001;Rahn et al, 2002bRahn et al, , 2003Röckmann et al, 2003;Rhee et al, 2006a;Feilberg et al, 2007;Rhee et al, 2008;Röckmann et al, 2010a,b;Vollmer et al, 2010;Walter et al, 2011;Haumann et al, 2012), as well as the isotope effects in the H 2 uptake by soils (Gerst and Quay, 2001;Rahn et al, 2002a;Rice et al, 2011). Two chemical transport models have been adapted to incorporate the stable isotopic composition of H 2 , namely GEOS-CHEM (Price et al, 2007) and TM5 (Pieterse et al, 2009(Pieterse et al, , 2012, and many more δD data have become available for the validation of such models (Rice et al, 2010;Batenburg et al, 2011). However, for obvious practical reasons, most of these data were collected at ground level, and yield little information about processes higher up in the atmosphere, particularly in the Upper TroposphereLower Stratosphere (UTLS) region.…”

“…Here, air samples are routinely analyzed for χ (H 2 ) and δD with a Gas Chromatography Isotope Ratio Mass Spectrometry (GC-IRMS) system as described by Rhee et al (2004) following a day-to-day procedure as described by Batenburg et al (2011). Briefly, in each acquisition the H 2 is separated from the air matrix and isotopically analyzed in the following 4 steps.…”

Isotopic signatures of production and uptake of H<sub>2</sub> by soil

“…The data correction procedures and isotope calibration are similar to those described in Batenburg et al (2011). Four reference gases were used to determine the δD values of the samples.…”

“…Four reference gases were used to determine the δD values of the samples. Two of them with δD values of (+207.0 ± 0.3) ‰ and (+198.2 ± 0.5) ‰ were calibrated and used previously in Batenburg et al (2011). The other two new reference gases …”

The stable isotopic signature of biologically produced molecular hydrogen (H<sub>2</sub>)

“…Tropospheric H 2 is enriched in deuterium with δD ∼ +130 ‰, (Gerst and Quay, 2001;Rhee et al, 2006;Rice et al, 2010;Batenburg et al, 2011) compared to surface emissions from fossil fuel combustion and biomass burning (δD approximately −200 ‰ and −300 ‰, respectively) (Gerst and Quay, 2001;Rahn et al, 2002;Röckmann et al, 2010a;Vollmer et al, 2010). As originally proposed by Gerst and Quay (2001) from budget closure, the photochemical sources of H 2 are also enriched in deuterium with δD between ∼ +100 ‰ and +200 ‰, (Rahn et al, 2003;Röckmann et al, 2003Röckmann et al, , 2010bFeilberg et al, 2007;Nilsson et al, 2007Nilsson et al, , 2010Pieterse et al, 2009 (Novelli et al, 1999;Hauglustaine and Ehhalt, 2002;Ehhalt and Rohrer, 2009;Pieterse et al, 2011) the extreme deuterium depletion relative to ambient atmospheric H 2 makes it a quite important contributor to the isotope budget (Price et al 2007;Pieterse et al 2011).…”