The First Ground-Based Measurement of Atmospheric Carbonyl Sulphide over Addis Ababa (Ethiopia)

Abstract

Measurement of Carbonyl sulphide is very crucial to estimate the sulfur budget and is used as a tracer for the carbon cycle. Its simultaneous consumption with CO2 during photosynthesis by plant uptake makes it an ideal candidate for the partitioning of photosynthesis from respiration. This research provides the first ground-based abundance of OCS from a high-resolution Fourier Transform Infrared spectrometer over Addis Ababa (9o1’N, 38o76’E, an altitude of 2443 m.a.s.l.). We used PROFFIT95 to retrieve the vertical profile, average tropospheric and stratospheric mixing ratios, and column amount from the solar absorption spectra of OCS. Analysis of random and systematic error to retrieval shows that the total error contribution due to atmospheric and auxiliary parameters is less than 10%. The tropospheric and stratospheric average VMR in our site is 0.488 ppbv and 0.230 ppbv, respectively, with deviation from the global mean by 2.4% for tropospheric mixing ratio. The hourly variation of OCS particularly on 14, March 2010 shows slight accession from mid-morning to noon and reduction in the afternoon with a change in VMR of 0.019 ppbv. The tropospheric volume mixing ratio (in the unit of parts per billion by volume) and total column amount time series result from May 2009 to April 2010 show seasonal variation with maximum (0.60) in May and June, and minimum (0.37) in December and January. The total column amount reaches up to 8.5X1019 molecules/m2. The correlation between stratospheric tropopause level and the accession of stratospheric OCS level during hot season worth detail investigation to understand the variation of OCS besides taking long term measurement for trend analysis.