Assessing real-world emissions from buses and taxis is vital to comprehend their impact on urban air quality. Such vehicles differ significantly from the majority of the fleet owing to their higher mileage rates. However, few studies have focused on specifically assessing the emissions from this segment of the vehicle fleet. In this context, this study evaluated the real-world emissions of nitrogen oxides (NO_x) from in-use buses and taxis in Dublin, Ireland, using crossroad remote sensing technology. The remote sensing system was deployed at strategic locations throughout the city to capture on-road emissions from passing vehicles. The collected data included vehicle related information such as emission standard, make, and mileage, and pollutants including NO_x. Based on this data, analysis was aimed to understand the impact of Euro emission standard, ambient temperature, mileage, and make of the vehicle on NO_x emissions. The results reveal that the average emissions from taxis reduce by 37% from Euro 5 to Euro 6b, and average emissions from Euro 6 buses are 87% lower compared to Euro 5. The trends in emission factors (EFs) of buses and taxis were similar during summer and winter sampling. Moreover, on comparing the emissions from the top five taxi manufacturers, different trends in the emission factors were observed. Finally, the study found that the effect of vehicle mileage on emissions was unclear for both buses and taxis. In any case, these findings provide valuable insights into the real-world emission performance of the existing fleet of buses and taxis in Dublin and highlight the need for targeted measures to reduce emissions from these vehicles. The results can assist policymakers and urban planners in formulating evidence-based strategies to improve air quality in Dublin and other cities facing similar challenges.

Emissions from real-world driving are often higher than estimated emission levels based on Euro emissions standards and type-approval tests. Consequently, the air quality in cities has not improved as originally anticipated from fleet renewal and stringent emission regulations for newer vehicles. This paper presents the real-world emission factors (EFs) for in-use cars, taxis, vans, and buses obtained using on-road remote sensing in Dublin city, Ireland. EFs from both petrol and diesel Euro 6 vehicles were significantly improved compared to the EFs of older emission standard vehicles. The analyses indicated that the presence of a few high emitting older vehicles skewed the overall distribution of EFs. Detailed description of variations in EFs for individual pollutants based on changes in emission standards, location, and other driving characteristics were studied and reported, which provide justification for implementing policies targeting fleet renewal.