Ground-based FTIR spectrometer observation of nitrous oxide and its validation over addis ababa, Ethiopia

Since May 2009 high-resolution Fourier transform infrared (FTIR) solar absorption spectra are recorded at Addis Ababa (9.01^o N, 38.76^o E, 2443 m altitude above sea level) Ethiopia. The vertical distribution of nitrous oxide (N₂O) was deduced from the spectra by using the retrieval code PROFFIT (V9.5). Four microwindows were taken for N₂O in the range between 2481 to 2541 cm^-1 and regularly determined instrumental line shape (ILS) was applied. A detailed error analysis of the N₂O retrieval is performed. Averaging kernel of N₂O indicates that there is sufficient information coming from the measurements, particularly at lower altitude. The variability of retrieved total column amount and profiles are observed over seasonal and inter-annual time scale. In spring season, the total column amount and volume mixing ratios (VMR) profiles of N₂O have shown relative increase with respect to the other seasons. The short term variation of N₂O profiles has also observed due to the transport process. A comparison of FTIR measurement of N₂O vertical profiles are made with coincident measurements of MLS satellite. Between 15 to 33 km, the mean absolute differences for FTIR comparisons lie within a range of -0.048 ppmv to +0.028 ppmv, however, most frequent values are approximated to be within 0.027 ppmv. The mean relative differences are found to lie between +5.8 ppmv and -3.7 ppmv. This corresponds to relative deviation from the mean are ranging from 4.4% to 35.6%.