Stratospheric Aerosol Climatology from Sage 11 and Observation of its Deriver, Carbonyl Sulfide, over Equatorial Africa

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Date

2010-07

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Addis Ababa University

Abstract

The issues of climate change and its causes have become agenda of di erent governmental and non-governmental discussions. The major atmospheric components responsible for climate change are particulate matters (aerosols) and trace gases (mainly anthropogenic green house gases). The stratospheric aerosol climatology over Ethiopia from SAGE II data and carbonyl sul de (OCS) measurement from FTIR spectrometer over Addis Ababa are discussed in this thesis. The vertical pro les of aerosol extinction over Ethiopia were analyzed and the result shows seasonal variation of stratospheric aerosol distribution over Ethiopia. The total column stratospheric aerosol also shows seasonal variation with maximum value attained during Spring and minimum during Summer. The annual mean value of total column AOD is observed to be steadily increasing from 1984 to 2005, which revealed the increasing trend of stratospheric aerosols of both ne and course mode particles. Results from the monthly mean stratospheric aerosol size distribution show that the number density is maximum for months of maximum AOD values as expected however the observed trend is not signi cant. The Bruker IFS120M was installed at tropical site located in Addis Ababa, Capital of Ethiopia (9o10 ; 38o760 ; 2443 m.a.s.l.) and has been continuously operating since May, 2009. Nearly regular cell (HBr cell) measurements were taken using laboratory source to monitor the alignment of the instrument and its stability over time. The analysis of cell measurement using LINEFIT (LINEFIT12) software has indicated the performance of the instrument is very good. The data measured between May, 2009 to April, 2010 were analyzed and interpreted. The latest version of PROFFIT (PROFFIT95) was used to retrieve vertical pro les and total column values of carbonyl sul de from pressure dependent broadened spectra with the help of Tikhonov-Philips regularization method. The OCS VMR observed at Addis site reaches up to 0.6 parts per billion by volume (ppbv) and the total column amount reaches up to 8 1019 molecules=cm2. The total column and vertical pro le observed in our xi site is greater than the same quantity reported at Izana, Spain. The tropospheric and stratospheric mass of OCS is also estimated in gram and we found it to be 4.6056 Tg and 0.3427 Tg respectively which sum up to yield of 4.9484 Tg of total mass. The atmopheric life time of OCS in our region is estimated to be 4.1236 years. Because of its longer life time in the atmosphere (as compared to other sulfur containing compounds), it is transported to the stratosphere through the tropical tropopause by di erent mechanisms and latter converted to form stratospheric background sulfate aerosol layer, which in turn determines the Earth's radiation budget. 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 10%

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Carbonyl Sulfide, over Equatorial Africa

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