Diesel-fueled public transport vehicles and air pollution in Addis Ababa, Ethiopia: Effects of vehicle size, age and kilometers travelled

Emissions from diesel-fueled vehicles constitute a serious problem in developing countries. They are composed of substances that are harmful to human health and the environment such as carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). This article argues that emissions from diesel-fueled public transport vehicles in Addis Ababa are substantial due to the old age of most of the vehicles (generally over 20 years). The article investigates the emissions generated by different categories of public transport vehicles - minibuses, mid-sized buses, and large buses-and explores the effects of vehicle size, age, and kilometers travelled on emission levels. Analysis of data for 358 diesel-fueled vehicles collected randomly at different locations in the city revealed that 243 (67.9%) of them had emission levels beyond the standard threshold with their smoke opacity being greater than or equal to 41%. Of these, 45 (18.52%) registered 100% smoke opacity. This study shows that minibuses are the dominant air pollutant in the city compared to mid-sized buses and large buses with an average smoke opacity of 86.36%, which is above the United States Environmental Protection Agency (U.S. EPA) standard. Only 19.92% of minibuses meet the smoke opacity standard. In terms of passenger carrying capacity, one large bus may be equivalent to eight minibuses. Shifting from the use of minibuses to large buses for public transport therefore represents a huge savings in emission and significant reduction in traffic congestion. The findings of this study lend credence to the current policy of the Government of Ethiopia to impose huge taxes on imported second-hand minibuses and encourage the impor-tation of brand-new large buses. Moreover, the findings suggest that the government should enact polices and regulations that limit the age of public transport vehicles from mechanical safety and emissions control perspectives.