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Measurements of H at the high-altitude site of Jungfraujoch, Switzerland are reported upon for the period of August, 2005-November, 2009. The time series consists of measurements that are primarily representative of free tropospheric background conditions. Highest background H mixing ratios were observed in May, while the lowest were observed in November. The mean seasonal H peak-to-trough amplitude of 21 parts per billion (ppb, 10 dry air mixing ratio) at Jungfraujoch was considerably less than at other stations at similar latitudes and the seasonal minimum in November was comparatively delayed. These differences are primarily attributed to a dampening and delay of the surface soil sink signal during its vertical propagation to the free troposphere. Excess (mixing ratio minus corresponding baseline value) H (ΔH) and excess CO (ΔCO) displayed no significant correlation. This lacking correlation is attributed to H removal by soil during transport to Jungfraujoch, thereby significantly altering the ΔH/ΔCO ratio from traffic combustion sources, which is the largest source of anthropogenic H influencing measurements at Jungfraujoch. [ABSTRACT FROM AUTHOR]

Abstract: This study assesses individual-vehicle molecular hydrogen (H2) emissions in exhaust gas from current gasoline and diesel vehicles measured on a chassis dynamometer. Absolute H2 emissions were found to be highest for motorcycles and scooters (141±38.6mg km−1), approximately 5 times higher than for gasoline-powered automobiles (26.5±12.1mg km−1). All diesel-powered vehicles emitted marginal amounts of H2 (∼0.1mg km−1). For automobiles, the highest emission factors were observed for sub-cycles subject to a cold-start (mean of 53.1±17.0mg km−1). High speeds also caused elevated H2 emission factors for sub-cycles reaching at least 150km h−1 (mean of 40.4±7.1mg km−1). We show that H2/CO ratios (mol mol−1) from gasoline-powered vehicles are variable (sub-cycle means of 0.44–5.69) and are typically higher (mean for automobiles 1.02, for 2-wheelers 0.59) than previous atmospheric ratios characteristic of traffic-influenced measurements. The lowest mean individual sub-cycle ratios, which correspond to high absolute emissions of both H2 and CO, were observed during cold starts (for automobiles 0.48, for 2-wheelers 0.44) and at high vehicle speeds (for automobiles 0.73, for 2-wheelers 0.45). This finding illustrates the importance of these conditions to observed H2/CO ratios in ambient air. Overall, 2-wheelers displayed lower H2/CO ratios (0.48–0.69) than those from gasoline-powered automobiles (0.75–3.18). This observation, along with the lower H2/CO ratios observed through studies without catalytic converters, suggests that less developed (e.g. 2-wheelers) and older vehicle technologies are largely responsible for the atmospheric H2/CO ratios reported in past literature. [Copyright &y& Elsevier]