A Study on Spatial and Temporal Variability of Black Carbon in Urban and Rural Background in Rwanda

Abstract

Air pollution is an environmental problem because of its effects on the health and quality of life. Rwanda is currently facing severe air quality problems that is due to a rapid urbanization process, land use changes, socio-economic transformation and a high population growth. This study focused on the spatial and temporal variability of Black Carbon mass concentration in two different backgrounds. BC data was measured continuously for the period from 7th July to March 31st at CST, an urban background by using a BC 1054 Multi-spectrum BC Monitor and another at MUGOGO station a rural using Magee Scientific 7-wavelength Aethalometer. Diurnal, monthly, seasonal and day of the week trends and correlation with meteorological parameters (T, RH) were analyzed. From the analysis, the concentration of BC were significantly low in the rainy compared to the dry season. The maximum hourly mean in Kigali was 15.007±2.216 µg/m3compared to 10.252±1.649 µg/m3 at Mugogo. A weekend effect was observed in Kigali with a decrease of BC concentrations during the weekend likely resulting from the reduction of emission activities but at Mugogo, there is no effect as the activities responsible for the emission of BC are present throughout the week. A positive correlation was found between Black Carbon and CO (R=0.70) at Kigali. A weak negative (R=-0.2180) and positive(R=0.249) correlation were observed between BC and T, RH in Kigali respectively and no correlation was found between them in Mugogo Monthly variation was observed by having the maximum monthly concentrations in July of 6.40 µg/m3 and 3.99 µg/m3 and the lowest in October (3.12 µg/m3) and November (0.47 µg/m3) for Kigali and Mugogo respectively and higher values were reported at Kigali. As biomass is the dominant cooking fuel used in Rwanda and is likely to lead to the local pollution and adverse health impacts. Other alternative cooking fuels which are pollution free should be used and the use of renewable energy should be prioritized. As the present study only focused on 2 background areas, it is recommended that future work should be conducted in the remaining areas to get a better overall view on BC trends in Rwanda.