Spatio-temporal assessment of polluting emissions from transport commuting in Kenya: The first step to inform mitigation strategies

Transport decarbonization is part of global efforts to combat climate change. Urban growth and the increasing need for commuting contribute to emissions that harm both the environment and public health. In the Global South, commuting operations are predominantly characterized by (in)formal paratransit systems, which rely on outdated, less environmentally efficient vehicles. This paper assesses the emissions of CO₂, NOx, CO, and PM_2.5 exhaust in a congested commuting corridor within the Nairobi metropolitan region to identify where and when mitigation strategies should be prioritized. The emissions calculation methodology follows an activity-based approach, incorporating distance travelled and vehicle operational parameters as a function of travel speed. Due to the lack of formal transport operation data, the study relies on empirical data collection through counting and observation of commuting events along the corridor. The results reveal spatio-temporal dependencies, with higher emission levels observed during peak hours and in areas closer to the city centre. Emissions patterns reflect the intensity of operations, with increased frequency and duration of commuting trips leading to greater environmental impacts. These findings should inform public policy development aimed at reducing pollutant emissions. Similarly, decarbonization strategies, such as vehicle electrification, should focus on the most polluted time windows and corridor segments.