A 15 year record of high-frequency, in situ measurements of hydrogen at Mace Head, Ireland

Abstract

Abstract. Continuous high-frequency measurements of atmospheric molecular hydrogen have been made at Mace Head atmospheric research station on the west coast of Ireland from March 1994 to December 2008. The presented data provides information on long term trends and seasonal cycles of hydrogen in background northern hemispheric air. Individual measurements have been sorted using a Lagrangian dispersion model to separate clean background air from regionally polluted European air masses and those transported from southerly latitudes. No significant trend was observed in background northern hemispheric air over the 15 year record, elevations in yearly means were accounted for from large scale biomass burning events. Seasonal cycles show the expected pattern with maxima in spring and minima in late autumn. The mean hydrogen mole fraction in baseline northern hemispheric air was found to be 500.1 ppb. Air transported from southerly latitudes showed an elevation from baseline mean of 11.0 ppb, reflecting both the latitudinal gradient of hydrogen, with higher concentrations in the Southern Hemisphere, and the photochemical source of hydrogen from low northern latitudes. European polluted air masses arriving at Mace Head showed mean elevation of 5.3 ppb from baseline air masses, reflecting hydrogen's source from primary emissions like fossil fuel combustion. Forward modelling of transport of hydrogen to Mace Head suggests that the ratio of hydrogen to carbon monoxide in primary emissions is considerably less in non-traffic sources than traffic sources.

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

“…H 2 emissions (3−22 Tg yr −1 ) originating from nitrogen fixation in the continental and marine biosphere complete the sources. H 2 oxidation by free hydroxyl radicals (OH) and enzymatic H 2 destruction in soils must balance these sources because tropospheric H 2 does not show a significant long term trend (Grant et al, 2010). H 2 oxidation through OH accounts for 14 to 24 Tg yr −1 , which is equivalent to 15% to 25% of the total H 2 sink.…”

Greenhouse gas measurements from a UK network of tall towers: technical description and first results

“…There is an approximate 37 and 36 nmol mol -1 , for CO and H 2 respectively, northern hemisphere mid-latitude seasonal trend. CO 15 has winter maxima and summer minima, driven predominantly by anthropogenic emissions and the strength of the summertime OH sink (Grant et al, 2010b;Satar et al, 2016). H 2 has delayed spring maxima and autumn minima due to maximum summertime loss by OH oxidation and greatest rates of soil uptake in the summer and early autumn when soils are driest (Grant et al, 2010b).…”

“…The sample selection system is integrated within the GC-ECD system (Sect. 3.4) (Grant et al, 25 2010a;Grant et al, 2010b). The GC-ECD front-end system at MHD and TAC have a 10-port, 2- (Fig.…”

“…stainless steel packed with MS 5Å, 60/80 mesh) from contamination by gases which adsorb to the surface of the main column and the main column separates H 2 and CO (Grant et al, 2010a). After separation, gases are injected into the RGA for analysis using zero air plus (Air Products, UK) carrier gas, where the samples pass over a heated bed of mercuric oxide before being quantitatively determined using UV 10 photometry (Grant et al, 2010a;Grant et al, 2010b). …”

“…H 2 is an important indirect GHG, due to its photochemical reaction with hydroxyl radicals (OH) in the troposphere reducing OH mole fractions, thus increasing the lifetime of CH 4 and affecting ozone production (Grant et al, 2010a;Grant et al, 2010b;Luan et al, 20 2016). Atmospheric mole fractions of CO 2 , CH 4 , N 2 O, SF 6 and CO have all exceeded pre-industrial levels due to anthropogenic activities (Kirschke et al, 2013;Stocker et al, 2013;Le Quéré et al, 2015).…”