Long-term in-use NOx emissions from London buses with retrofitted NOx aftertreatment
File(s)
Accepted version
Author(s)
Phantawesak, Napameth
Coyle, Finn
Stettler, Marc
Type
Journal Article
Abstract
Buses constitute a significant source of air pollutant emissions in cities. In this study, we present real-world NOx emissions from 97 diesel-hybrid buses measured using on-board diagnostic systems over 44 months and 6.35 million km in London. Each bus had previously been retrofitted with a selective catalytic reduction (SCR) aftertreatment system to reduce emissions of nitrogen oxides (NOx). On average, parallel hybrid (PH) and series hybrid (SH) buses emitted 3.80 g of NOx/km [standard deviation (SD) of 1.02] and 2.37 g of NOx/km (SD of 0.51), respectively. The SCR systems reduced engine-out emissions by 79.8% (SD of 5.0) and 87.2% (SD of 2.9) for the PHs and SHs, respectively. Lower ambient temperatures (0–10 °C) increased NOx emissions of the PHs by 24.2% but decreased NOx emissions of the SHs by 27.9% compared to values found at more moderate temperatures (10–20 °C). To improve emissions inventories, we provide new distance-based NOx emissions factors for different ranges of ambient temperature. During the COVID-19 pandemic, the emissions benefits of reduced congestion were largely offset by more frequent route layovers leading to lower SCR temperatures and effectiveness. This study shows that continuous in-service measurements enable quantification of real-world vehicle emissions over a wide range of operations that complements conventional testing approaches.
Date Issued
2022-06-07
Date Acceptance
2021-10-13
Citation
Environmental Science and Technology (Washington), 2022, 56 (11), pp.6968-6977
ISSN
0013-936X
Publisher
American Chemical Society
Start Page
6968
End Page
6977
Journal / Book Title
Environmental Science and Technology (Washington)
Volume
56
Issue
11
Copyright Statement
© 2021 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science and Technology, after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.est.1c05083
Subjects
NOx emissions
catalytic reactions
environmental pollution
heavy-duty diesel vehicles
redox reactions
sensors
temperature dependence
Air Pollutants
COVID-19
Gasoline
Humans
London
Motor Vehicles
Pandemics
Vehicle Emissions
Humans
Air Pollutants
Gasoline
Vehicle Emissions
Motor Vehicles
London
Pandemics
COVID-19
Environmental Sciences
Publication Status
Published
Date Publish Online
2021-10-27