Vehicular exhaust emissions from road transport that substantially contribute to air pollution along Thika superhighway, Kenya

Abstract

Road transportation is one of the anthropogenic sources of greenhouse gases (GHGs) and other air pollutants in Kenya, which have a serious negative impact on human health.  The fact that traffic emissions happen directly at ground level in crowded urban areas and expose millions of people to dangerous pollutants like particulate matter (PM₂.₅), nitrogen oxides (NOₓ), volatile organic compounds (VOCs) among others, at concentrations significantly higher than those from industrial or natural sources makes them a more serious concern than many other emission sources. For the purpose of developing and implementing relevant policies and technology for adequate mitigation measures, an emission inventory needs to be created. The aim of the current study is to estimate the vehicular emissions from different vehicle categories using Thika Superhighway as a case study. The correlation between vehicle population, emission factors, and vehicle kilometer travelled and the levels of emissions were analyzed by use of qualitative and quantitative methods. The bottom-up approach method was used in this study. A total of 398 vehicles were sampled, which included two wheelers, three wheelers, cars and SUVs, Buses, light motor vehicle (passengers), light motor vehicles (goods) and heavy-duty vehicles (HMV).  This study reported that the total vehicular emissions of NO_X, CO, NMVOC, NH₃, PM₁₀, PM_2.5, black carbon (BC) and organic carbon (OC) are 1,971.501, 2,232.053, 293.514, 19.543, 80.080, 80.080, 45,437.969, 1,772.328 t/year, respectively. From the study, buses were the highest contributors of NO_X, PM₁₀, PM_2.5 and BC emissions, whereas two-wheelers accounted for the majority of CO and NMVOC emissions. LMV passenger (diesel) accounted for the majority of NH₃ and OC emissions.  Implementation of car-free days, use of hybrid and electric vehicles and introduction of policies that aim at eliminating unroadworthy automobiles are some of the policies which are recommended to minimize vehicular emissions in Nairobi County.