Ozone, carbon monoxide and nitrogen oxides time series at four alpine GAW mountain stations in central Europe

Abstract

Long-term, ground based in-situ observations of ozone (O₃) and its precursor gases nitrogen dioxide (NO₂) and carbon monoxide (CO) from the four sites Hohenpeissenberg and Zugspitze (D), Sonnblick (A) and Jungfraujoch (CH) are presented for the period 1995–2007. These Central European alpine mountain observatories cover an altitude range of roughly 1000 to 3500 m. Comparable analytical methods and common quality assurance (QA) procedures are used at all sites. For O₃ and CO, calibration is linked to primary calibrations (O₃) or CO standards provided by the Central Calibration Laboratory (CCL) at NOAA/ESRL. All stations have been audited by the World Calibration Centre (WCC) for CO and O₃ (WCC-Empa; CH). Data from long-term measurements of NO₂ and CO are only available from Hohenpeissenberg and Jungfraujoch. Both sites show slightly decreasing mixing ratios of the primarily emitted NO₂ and the partly anthropogenically emitted CO between 1995 and 2007. The findings are generally consistent with shorter observation periods at Zugspitze and Sonnblick and thus are considered to represent regional changes in Central European atmospheric composition at this altitude range. Over the same period, 1995–2007, the O₃ mixing ratios have slightly increased at three of the four sites independent of wind sector. Trends are often more pronounced in winter and less in summer; highest declines of NO₂ and CO are observed in winter and the lowest in summer, whereas the strongest O₃ increase was detected in winter and lowest or even decline in summer, respectively. Weekly cycles demonstrate anthropogenic impact at all elevations with enhanced NO₂ on working days compared to weekends. Enhanced O₃ values on working days indicating photochemical production from anthropogenic precursors are only observed in summer, whereas in all other seasons anti-correlation with NO₂ was found due to reduced O₃ values on working days. Trends are discussed with respect to anthropogenic impacts and vertical mixing. The observed trends for NO₂ at the alpine mountain sites are less pronounced than trends estimated based on emission inventories.