Batenburg, Anneke M; Popa, M Elena; Vermeulen, Alexander T; Van den Bulk, Willem CM; Jongejan, Piet AC; Fisher, Rebecca E; Lowry, David; Nisbet, Euan G; Röckmann, Thomas (2016): Molecular hydrogen (H2) mixing ratio and stable isotopic composition (dD) at the Cabauw tall tower in the Netherlands (2008-2012) [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.864969,

---

Supplement to: Batenburg, AM et al. (2016): Observations of molecular hydrogen mixing ratio and stable isotopic composition at the Cabauw tall tower in the Netherlands. Atmospheric Environment, 147, 98-108, https://doi.org/10.1016/j.atmosenv.2016.09.058

Measurements of the stable isotopic composition (dD(H2) or dD) of atmospheric molecular hydrogen (H2) are a useful addition to mixing ratio (X(H2)) measurements for understanding the atmospheric H2 cycle. dD datasets published so far consist mostly of observations at background locations. We complement these with observations from the Cabauw tall tower at the CESAR site, situated in a densely populated region of the Netherlands. Our measurements show a large anthropogenic influence on the local H2 cycle, with frequently occurring pollution events that are characterized by X(H2) values that reach up to 1 ppm and low dD values. An isotopic source signature analysis yields an apparent source signature below -400 per mil, which is much more D-depleted than the fossil fuel combustion source signature commonly used in H2 budget studies. Two diurnal cycles that were sampled at a suburban site near London also show a more D-depleted source signature (-340 per mil), though not as extremely depleted as at Cabauw. The source signature of the Northwest European vehicle fleet may have shifted to somewhat lower values due to changes in vehicle technology and driving conditions. Even so, the surprisingly depleted apparent source signature at Cabauw requires additional explanation; microbial H2 production seems the most likely cause. The Cabauw tower site also allowed us to sample vertical profiles. We found no decrease in (H2) at lower sampling levels (20 and 60m) with respect to higher sampling levels (120 and 200m). There was a significant shift to lower median dD values at the lower levels. This confirms the limited role of soil uptake around Cabauw, and again points to microbial H2 production during an extended growing season, as well as to possible differences in average fossil fuel combustion source signature between the different footprint areas of the sampling levels. So, although knowledge of the background cycle of H2 has improved over the last decade, surprising features come to light when a non-background location is studied, revealing remaining gaps in our understanding.

Please cite the original AtmosEnv article (doi:10.1016/j.atmosenv.2016.09.058) when using these data.

The paper also contains more information about how these data were collected and calibrated, and on how the quality control flags were assigned.

All samples were collected at the Cabauw tower, at the CESAR site (51.971° N, 4.927° E, http://www.cesar-observatory.nl/). H2 and deltaD(H2) are calibrated using one to four laboratory reference air cylinders, depending on measurement period. The H2 mixing ratio of the reference cylinders was determined by UHEI-IUP, MPI-BGC, or the IMAU isotope laboratory. The deltaD(H2) of the reference cylinders is, sometimes indirectly, linked to the VSMOW scale by measurements of air mixtures containing H2 standards of known isotopic composition.

H2 scale: MPI2009, Jordan and Steinberg, AMT, 2011, doi:10.5194/amt-4-509-2011

deltaD(H2) units: permil deviation from VSMOW, Gonfiantini et al., IAEA-TECDOC-825, IAEA