Application of Gas Chromatography with a Pulsed Discharge Helium Ionization Detector for Measurements of Molecular Hydrogen in the Atmosphere

The Earth's troposphere contains approximately 160 Tg H-2 with an average surface mixing ratio similar to 530 nmole mole(-1) (ppb) and lifetime of 2 years. Atmospheric H-2 is typically measured using gas chromatography (GC) followed by hot mercuric oxide reduction detection (GC-HgO). Here we describe an alternate method using GC with a pulsed-discharge helium ionization detector (HePPD). HePPD is a universal detector; when applied to H-2, the GC-HePDD provides a wide linear range (0.3% over a range of 2000 ppb), a detection limit of similar to 0.03 pg, high precision (0.12%) and a stable response (+/- 1.6% over nearly one year). HePPD is compared to HgO reduction using a suite of gravimetrically prepared reference gases spanning remote to urban concentrations. The method is excellent for atmospheric measurements as it provides a wide linear range with high precision, stability and reproducibility. We suggest these characteristics will improve the ability to maintain reference gases and improve measurements of atmospheric H-2, thus providing better constraints on potential future changes in its sources and sinks.