Dust Characterization and Evaluation of Indoor Environmental Quality (IEQ): Case Study of AFTU Buses in Senegal

Africa is experiencing a high urbanization rate, ~4% with megacities emerging like Cairo in Egypt, Lagos in Nigeria, Kinshasa in Democratic Republic of Congo. In parallel, a deterioration in air quality is being witnessed. Road traffic contributes significantly to atmospheric pollution through unregulated traffic, poor roads’ design, poor fuel quality and surge in vehicle imports. Arica is the continent with lowest roads densities and with most unpaved roads. Congestion is now frequent in cities with adverse consequences on the economy, health, and society. High daily temperature observed in tropical climates, and favourable wind speed favour dust resuspension and Sahara dust dispersion. Literature review shows a less focus on in-cabin dispersion and impacts. The present work regards a study of the indoor environmental quality (IEQ) of the public transport buses provided by the AFTU company in the city of Thiès, in Senegal. A Particle Plus 8301-AQM2 Series handled optical particle counter (OPC) was used as it offers a good characterisation of the fine particles. the outdoor air, the vehicle itself and the occupants were identified main pollutants sources. Fine particles concentrations, carbon dioxide (CO₂), temperature and relative humidity were recorded on several routes at different periods of the day and for several days during the rainy season. Recorded data show high concentration of PM_2.5 which increases over time (from 25 up to 300 µg/m³) depending on outdoor conditions and the areas crossed by the vehicle. Variations of PM concentration in different channels: 0.5, 1, 2.5, 5 and 10 were also analysed. Recorded values showed very small mass fraction of 0.5 and large proportion of 5-10 µm diameter particles. CO₂ concentration (300-900 ppm) varies with the number of passengers during the trip. The temperature was above 30 °C and the relative humidity, in the range 40-70%. The speed analysis shows high frequency variations and was found low, ~2.5 m/s. A conclusion that emerged is that keeping doors and windows open help in eliminating excess CO₂ but ends in high level of particulate matter concentration in the cabin.