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

Semi-continuous measurements of atmospheric molecular hydrogen (H-2) 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 H-2 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 H-2 mixing ratios, the absolute levels as well as the seasonal amplitude agree well with literature data from semi-rural and remote sites. The H-2 dry deposition velocity for summer days with low winds is estimated to be between 0.5 x 10(-4) to 1 x 10(-4) m s(-1). Diurnal cycles are dominated by H-2 emissions from nearby traffic. The influence of traffic-related emissions is also corroborated by a high H-2 to CO correlation. Typical molar H-2 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 H-2 emissions is estimated for a period covering the last 25 years. Since the ambient H-2 concentration did not decline during the same period, other simultaneous changes of sinks or sources of H-2 must have compensated this reduction. (c) 2006 Elsevier Ltd. All rights reserved.