Infrared spectroscopy of tropospheric trace gases: combined analysis of horizontal and vertical column abundances

Vibration-rotation absorptions in high-resolution Fourier-transform infrared spectra from a 246-m horizontal path were used to derive local concentrations of trace gases at the Alpine observatory at the Zugspitze summit, Germany (2964 m above sea level). The analysis was performed by using the line-by-line nonlinear least-squares spectral fitting software, SFIT, based on the 1992 HITRAN line parameter compilation. (HITRAN is a high-resolution transmission molecular absorption database.) A comparison to in situ measurements shows an agreement of better than 4.3% for the species CO, CO(2), and CH(4). Using the same spectrometer and analysis software, we obtained the vertical column density of N(2)O together with an adjusted vertical volume mixing ratio distribution. This translates to a local N(2)O concentration at the altitude of Zugspitze that agrees with the horizontal path-derived value to within 1%.