First year of atmospheric hydrogen measurements and source fingerprinting at the ICOS Lutjewad Station

Molecular hydrogen (H₂) plays an important role in atmospheric chemistry and is considered an indirect greenhouse gas through its influence on methane's lifetime and tropospheric ozone formation. With the anticipated expansion of a hydrogen-based economy, establishing background concentrations and identifying present-day emission sources are essential for detecting and attributing future changes. In this study, we present a one-year record of continuous atmospheric H₂ measurements conducted at the ICOS atmospheric station Lutjewad, located in the north of the Netherlands. Atmospheric H₂ mole fractions were measured using a gas chromatograph with a pulsed discharge helium ionization detector (GC-PDHID) sampling dried ambient air from a 60 m tall tower, alongside measurements of CH₄, CO₂, N₂O, and CO used for source fingerprinting of the observed H₂ enhancements. Field campaigns at regional source locations were conducted to investigate the potential emission sources, including traffic emissions (tunnel measurements), methanogenic sources (landfills), and cattle farms. Furthermore, we investigated the potential of the Radon Tracer Method (RTM) to infer regional hydrogen emissions. We observe that continental air masses lead to pronounced atmospheric H₂ enhancements (up to 700 ppb), whereas northerly (marine) winds consistently represent clean background conditions (490–540 ppb), comparable to the observations at the European continental background station Mace Head on the east coast of Ireland. We present results of our on-going Jena sausage flask intercomparison programme which includes hydrogen measurements (once every 4 months), allowing for an independent quality control of the accuracy of our hydrogen measurements in the atmospheric range of 410 – 630 ppb H₂.

Overall, this work establishes a pre–hydrogen economy baseline for atmospheric H₂ in northwestern Europe. Our continuous observations proof to be fundamental for a better understanding of H₂ sources within the footprint of our station and a starting point for monitoring emission changes associated with the emerging hydrogen economy.