Tracking isotopic signatures of CO2 at the high altitude site Jungfraujoch with laser spectroscopy: analytical improvements and representative results

摘要

We present the continuous data record of atmospheric CO isotopes measuredby laser absorption spectroscopy for an almost four year period at the HighAltitude Research Station Jungfraujoch (3580 m a.s.l.), Switzerland. The meanannual cycles derived from data of December 2008 to September 2012 exhibitpeak-to-peak amplitudes of 11.0 μmol mol for CO,0.60‰ for δC and 0.81‰ for δO. Thehigh temporal resolution of the measurements also allow us to capture variationson hourly and diurnal timescales. For CO the mean diurnal peak-to-peakamplitude is about 1 μmol mol in spring, autumn and winterand about 2 μmol mol in summer. The mean diurnalvariability in the isotope ratios is largest during the summer months too,with an amplitude of about 0.1‰ both in the δC andδO, and a smaller or no discernible diurnal cycle during theother seasons. The day-to-day variability, however, is much larger anddepends on the origin of the air masses arriving at Jungfraujoch. BackwardLagrangian particle dispersion model simulations revealed a close linkbetween air composition and prevailing transport regimes and could be used toexplain part of the observed variability in terms of transport history andinfluence region. A footprint clustering showed significantly differentwintertime CO, δC and δO values depending on theorigin and surface residence times of the air masses.Several major updates on the instrument and the calibration procedures were performed in order tofurther improve the data quality. We describe the new measurement andcalibration setup in detail and demonstrate the enhanced performance of theanalyzer. A measurement precision of about 0.02‰ for both isotope ratios hasbeen obtained for an averaging time of 10 min, while the accuracy was estimated to be 0.1‰,including the uncertainty of the calibration gases.