Evaluation of indoor environmental quality (IEQ) of transport cabins using optical particle counters

Africa is experiencing an unprecedented demographic growth since few decades. It is followed by an increasing rate of urbanization in almost all countries. In parallel, we are witnessing a deterioration in air quality, especially in urban areas. Road traffic contributes significantly to atmospheric pollution through unregulated traffic, poor roads’ design, and poor fuel quality. The surge in vehicle imports appears as an aggravating factor, as these vehicles are old and use low quality fuels. Roads’ densities are very low, most roads unpaved or poorly maintained. Congestion has become frequent in new megacities such as Dar-es-Salam, Lagos, Douala, Abidjan, etc. Literature review shows a focus on outdoors dispersion and impacts and points out exhaust fumes, tyres degradation, and roads condition as main sources of pollutants while studies focusing on in-cabin pollution are still scarce. In this study, we present results of an ongoing evaluation of air pollutants concentration in minibuses in the city of Thiès (Senegal) using a Particle Plus 8301-AQM2 Series handled optical particle counter (OPC). Three different types of sources are identified, as the outdoor air, the vehicle itself and the
occupants. Fine particles concentrations, carbon dioxide (CO2), temperature and relative humidity were recorded in several routes at different periods of the day (morning, afternoon, and evening) and for several days. Recorded data show high concentration of fine particles which increases over time (from 25 up to 300 µg/m3) depending on outdoor conditions and the areas crossed by the bus. CO2 concentration (300-900 ppm) varies with the number of passengers during the trip. The temperature was in the range 30-40 °C and the relative humidity, 40-70%. The speed analysis shows frequent variations and was found low, ~2.5 m/s. Keeping doors and windows open help in eliminating excess CO2 but ends in high level of dust concentration in the cabin.