Projecting impacts of two-wheelers on urban air quality of Douala, Cameroon Cyrille Mezoue Adiang a,b , David Monkam b , Ebenezer Njeugna c , Sharad Gokhale d,⇑ a Faculty of Industrial Engineering, University of Douala, P.O. Box: 2701, Douala, Cameroon b Faculty of Science, University of Douala, P.O. Box: 24157, Douala, Cameroon c Advanced Teachers Training College for Technical Education, University of Douala, P.O. Box: 1872, Douala, Cameroon d Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India article info Article history: Keywords: Cameroon World Bank Carbon monoxide Urban air quality Euro emissions standards Urban traffic abstract Douala, one of the fastest developing cities of Cameroon, has been experiencing unprece- dented growth of two-wheelers (motorbikes) and poor perceived air quality. The city has no air quality monitoring system and no air quality data. The only survey that reported the carbon monoxide (CO) levels was carried out by the World Bank under the Clean Air Initiative in 2002 and another study of traffic counts in 2008. In this study, the World Bank CO concentration levels of 2002 have been validated by back projecting the 2008 traf- fic scenario using vehicular emission and line source dispersion models and future scenar- ios up to 2015 have been projected at one of the busiest traffic intersections. The potential impacts of Euro emissions standards to improve the roadside air quality in Douala were studied. The results showed that the CO levels increased by a factor of 18 for a period from 2002 to 2015 with an annual increase of 65% in two-wheelers and 31% in cars. The esti- mated population of two-wheelers in 2015 was found to be 23 times higher than in 2002, which, by 2035, is expected to grow by 533% and the car ownership by 146%. If Euro II and III emissions standards are gradually implemented on two-wheelers in Cameroon, CO levels along roadways are expected to be reduced by about 70%. These results may be helpful to policy makers to prepare an air quality management plan for the city. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Unprecedented growth in the number of vehicles led by increasing population in rapidly urbanising cities has contributed to the growing problems of air quality throughout the African continent and developing countries (Shiva Nagendra et al., 2016; UNEP, 2005). In Cameroon, in 2005, 48.8% of the population lived in urban areas such as Douala, the economic capital (BUCREP, 2011). The growth in vehicles is mainly seen in two-wheelers, a new mode of transport in Cameroon, where two- wheelers are used as taxis, called ‘ben skin’ locally (Olvera Diaz et al., 2007; Sahabana, 2006). The major share of two- wheelers in the traffic is due to the shortage of public transport, inadequate road infrastructure, and a loose regulatory framework (Olvera et al., 2012). Most of the motorbikes in Cameroon are imported from Asian countries, particularly China and there are no clear regulations for emissions standards (CUD, 2008; Khan et al., 2009; Sietchiping et al., 2012). http://dx.doi.org/10.1016/j.trd.2017.02.010 1361-9209/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: sharadbg@iitg.ernet.in (S. Gokhale). Transportation Research Part D 52 (2017) 49–63 Contents lists available at ScienceDirect Transportation Research Part D journal homepage: www.elsevier.com/locate/trd