Perennial observations of molecular hydrogen (H2) at a suburban site in Switzerland

Semi-continuous measurements of atmospheric molecular hydrogen (H2) and carbon monoxide (CO) were performed at a suburban sampling site in Switzerland from November 2002 to February 2005. The presented data provide information about time series, seasonal and diurnal cycles as well as sources and sinks in a suburban environment. Such records become increasingly important for the assessment of the effects of a possible future hydrogen economy on the environment. No significant trend of background H2 concentrations could be observed for the considered period. Seasonal cycles show the expected pattern with maxima in winter and minima in summer and autumn. When extracting the background H2 mixing ratios, the absolute levels as well as the seasonal amplitude agree well with literature data from semi-rural and remote sites. The H2 dry deposition velocity for summer days with low winds is estimated to be between 0.5×10-4 to . Diurnal cycles are dominated by H2 emissions from nearby traffic. The influence of traffic-related emissions is also corroborated by a high H2 to CO correlation. Typical molar H2 to CO ratios from traffic were found to be 0.33 on a molar basis (ppb/ppb). A reduction of 37–62% in European anthropogenic H2 emissions is estimated for a period covering the last 25 years. Since the ambient H2 concentration did not decline during the same period, other simultaneous changes of sinks or sources of H2 must have compensated this reduction.