Evaluating impacts of two-wheeler emissions on roadside air quality in the vicinity of a busy traffic intersection in Douala, Cameroon

Air quality is deteriorated due to heavy traffic in the urban centers of Cameroon in Central Africa. The Douala city has witnessed unprecedented growth of vehicles, particularly motorbikes (two-wheelers), which are the primary cause of roadside pollutants. However, the menace of pollution, due to the use of old cars over 12 years, continues. The main objective of this study has been to evaluate the impacts of two-wheelers and old cars on the pollutants originated at the Ndokoti intersection in Douala using a combine field and air quality modeling and assess the effect on urban population. The study uses a semi-empirical model to compute vehicular emission rate, the Gaussian plume model for pollutants dispersion, and the Robust Uniform World Model for assessing impacts of pollutant levels on urban population. The results show that during traffic jam, the concentrations of CO and NO2 increase with the age of cars and found to be higher with the increase in number of two-wheelers. Using models, scenarios such as a car plying together with 2, 4, 6, and 8 two-wheelers have been developed to determine the influence of the two-wheelers on the pollutant concentration. The estimated pollutant concentrations match well with the measured concentrations. The average roadside CO concentration increases from 60 (scenario 1) to 180 mg m−3 (scenario 5), indicating the prominent impact of two-wheelers on air quality. The comparison of the roadside concentrations in Douala and the guidelines of the WHO show that a large exceedance of up to about 300%, depending on the scenario.