Atmospheric concentration of selected trace gases over Uganda

Abstract

The atmospheric concentration of the trace gases of CO2, CH4, NO2 and SO2 over Uganda was obtained at the stations of Makerere, Mukono, Lira, Tororo and Kasese. Data used in this study was retrieved from the Ozone Monitoring Instrument (OMI) sensor aboard the Aura Satellite, the Atmospheric Infrared Sounder (AIRS) aboard the Aqua satellite and the Ground based instruments (Combo Diffusion tubes). During the study analysis, monthly and annual averages were obtained from which for example CO2 for Makerere/Mukono, Lira, Tororo and Kasese had annual averages of about (388.9 ± 8.2), (388.7 ± 8.5), (388.9 ± 8.3) and (388.8 ± 8.2) ppmv yet the SO2 concentration for the stations ofMakerere, Mukono, Lira, Tororo and Kasese were (0.65 ± 0.07), (0.63 ± 0.08), (0.61 ± 0.06), (0.69 ± 0.27) and (0.60 ± 0.08) DU respectively. From the developed averages, the highest and lowest concentrations were obtained and accounted for after which the respective concentration maps were as well generated. Seasonally, it was observed that the selected trace gases vary according to the weather season of the year as well like CH4 concentration increased in the months of February and November which are known to be sunny months with relatively high temperatures. Although all the obtained concentrations were still generally below the limits in the published papers, measures must be put to check on the steadily improving concentration levels. The comparison between the ground-based measurements and the satellite overpass data gave comparable results with a relatively small percentage difference. For example, the institute of public health - Mulago had an average ground based measurement of about 1.76 μg/m3 yet the satellite overpass average was about 1.26 μg/m3 which resulted into a percentage discrepancy of about 28.4%