In-situ measurements of oxygen, carbon monoxide and greenhouse gases from Ochsenkopf tall tower in Germany

Abstract

We present 2.5 years (from June 2006 to December 2008) of in-situ measurements of CO₂, O₂, CH₄, CO, N₂O and SF₆ mixing ratios sampled from 23, 90 and 163 m above ground on the Ochsenkopf tower in the Fichtelgebirge range, Germany (50°01'49" N, 11°48'30" E, 1022 m a.s.l.). In addition to the in-situ measurements, flask samples are taken at Ochsenkopf at approximately weekly intervals and are subsequently analysed for the mixing ratios of the same species, as well as H₂, and the stable isotopes, δ¹³C, δ¹⁸O in CO₂. The in-situ measurements of CO₂ and O₂ from 23 m show substantial diurnal variations that are modulated by biospheric fluxes, combustion of fossil fuels, and by diurnal changes in the planetary boundary layer height. Measurements from 163 m exhibit only very weak diurnal variability, as this height (1185 m a.s.l.) is generally above the nocturnal boundary layer. CH₄, CO, N₂O and SF₆ show little diurnal variation even at 23 m owing to the absence of any significant diurnal change in the fluxes and the absence of any strong local sources or sinks. From the in-situ record, the seasonal cycles of the gas species have been characterized and the multi-annual trends determined. Because the record is short, the calculation of the trend is sensitive to inter-annual variations in the amplitudes of the seasonal cycles. However, for CH₄ a significant change in the growth-rate was detected for 2006.5–2008.5 as compared with the global mean from 1999 to 2006 and is consistent with other recent observations of a renewed increasing global growth rate in CH₄ since the beginning of 2007.