Evaluation of the Impact of Motorcycles in Urban Transport on Air Pollution: A Case of Douala City in Cameroon

Aims: This work aimed to evaluate the impact of motorcycle taxis on air pollution for the particular case of Douala city in Cameroon.

Study Design: Samples were collected from motorcycle drivers and an exhaust gas analyser was used for better understanding of this area of ​​activity. It was done to obtain the different amounts of pollutants emitted by these motorcycles in different traffic situations.

Place and Duration of Study: Douala Urban Community, National Advanced School of Public Works, and Energy, Water and Environment Laboratory of National Advanced School of Engineering (University of Yaounde I) between February 2017 and June 2018.

Methodology: The statistical data concerning the motorcycles in circulation, estimated around 233,799, in the transport sector between 2009 and 2013 in Cameroon, were used for the present study. Using these data, the correlation of the evolution of motorcycles in circulation in the transport sector was established. For motorcycles exhausts, atmospheric pollutants namely, carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxide (NOx) and hydrocarbon (HC) were measured.

Results: A survey of 500 motorcycle taxis, revealed that 58% of motorcycles were acquired prior to release, 56% was less than 5 years old and 95% consumed gasoline. The survey also revealed that 64% of motorcycles operating in urban transport had a tax power of between 6 and 7 HP. The different amounts of pollutants, emitted on a sample of 45 motorcycle taxis, followed that in slow traffic in urban areas (5 km/h), CO (depending on their aging condition) was emitted between 0.40 and 3.02 g/kg; the Euro 3 standard on motorcycle emissions recommends a limit of 1 g/kg. In the same traffic situation, maximum values ​​for HC and NOx, were 0.62 g/kg and 3.10×10‑3 g/kg, respectively; values ​​were within the limits set by the same standard, namely 0.8 g/kg and 0.15 g/kg respectively. The statistics available between 2007 and 2011 revealed an almost linear evolution of the "motorcycle" phenomenon in urban centers in Cameroon, making it possible to put 647,000 motorcycles into circulation between 2007 and 2018.

Conclusion: Traffic situation, aging of the motorcycles and nature of the fuel revealed their influence on the emissions of pollutants by motorcycle taxis. These results are a useful tool to monitor the air pollution levels caused by motorcycles in urban transport.