Observation and Validation of No and No2 from Ftir Over Addis Ababa

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Addis Ababa University


Since May 2009 atmospheric absorption spectra using the sun as the source of radiation have been recorded by a ground-based high spectral resolution FTIR spectrometer (Bruker IFS120 M). The alignment of the instrument and its stability over time is monitored by nearly regular cell (HBr) measurements. The analysis of this cell measurement using LINEFIT (Version 12) software has indicated the performance of the instrument is very good. The data measured from May, 2009 to February, 2011 were analyzed and interpreted. The latest version of PROFFIT (PROFFIT95) was used to retrieve vertical pro les for NO and NO2 and their column amount from pressure dependent broadened spectra with the help of Tikhonov-Philips regularization method. Finally total mean daily and monthly column amount of NO2 is validated with OMIL3 satellite data. The NO and NO2 VMRs observed at Addis site reach values of 9.247 ppbv and 2.76 ppbv respectively. Both gases are highly dependent on day time solar strength. The maximum partial column amount on 30, May 2009 occured in between 22.1-23.436 km for NO2 in lower stratosphere and 32.366-34.22 km for NO in middle stratosphere. The concentration of NOx (NO+NO2) life time highly depends on the solar zeinth angle. Random and systematic error contribution to retrieval were analyzed and the result shows that the total error contribution due to atmospheric and auxiliary parameters is less than 34.54% for NO and 38.62% for NO2. The validation of NO2 with that from OMIL3 was complicated by the fact that OMIL3 measurement are taken during the whole day while FTIR measurements are mostly from 9-14 LST. As a result OMILS NO2 is expected to be higher than FTIR NO2 which is indeed found to be the case in this work



Observation and Validation