Real-world NOx emissions from passenger vehicles and buses
File(s)
Author(s)
Phantawesak, Napameth
Type
Thesis
Abstract
Outdoor air pollution is responsible for 4.2 million premature deaths worldwide and 99% of the
global population were living in areas that exceeded the World Health Organisation air quality
guidelines in 2019. Road transport is a major source of oxides of nitrogen (NOx). Exceedances of
the annual mean concentration limit for nitrogen dioxide (NO2) in major cities have been largely
attributed to the discrepancies between type approval limits and real-world driving emissions.
To improve our understanding and models for real-world NOx emissions from road transport, this
thesis utilises on-road NOx emissions data from 97 Euro V SCR retrofitted buses and the largest
Portable Emissions Measurement System (PEMS) dataset to date, comprising of 826 Euro 5 and
Euro 6 passenger vehicles. For each vehicle class, the impact of driving dynamicity, external
conditions (such as ambient temperature) and, where applicable, the effectiveness of the NOx
aftertreatment system on NOx emissions are examined to address the research gaps in the literature.
The effects of ambient temperature on NOx emissions were found to be highly dependent on the
type of hybrid system of the buses. As ambient temperature decreased from 10 – 20°C to 0 – 10°C,
NOx emissions for parallel hybrid increased by 24.2%. However, the same reduction in ambient
temperature resulted in a 27.9% decrease in NOx emissions for the series hybrid. Ambient
temperature is currently not accounted for in the emission inventories.
A new dynamic emissions model, REVS (Road transport Emissions and Variance Simulator) is
proposed to address the variability in NOx emissions arising from different driving dynamics at
the same average speed. When compared to NOx emission factors measured by PEMS, REVS
provided an average reduction in the percentage discrepancy of 43 percentage points compared to
Computer Program to Calculate Emissions from Road Transport (COPERT), the EU standard
vehicle emissions calculator.
global population were living in areas that exceeded the World Health Organisation air quality
guidelines in 2019. Road transport is a major source of oxides of nitrogen (NOx). Exceedances of
the annual mean concentration limit for nitrogen dioxide (NO2) in major cities have been largely
attributed to the discrepancies between type approval limits and real-world driving emissions.
To improve our understanding and models for real-world NOx emissions from road transport, this
thesis utilises on-road NOx emissions data from 97 Euro V SCR retrofitted buses and the largest
Portable Emissions Measurement System (PEMS) dataset to date, comprising of 826 Euro 5 and
Euro 6 passenger vehicles. For each vehicle class, the impact of driving dynamicity, external
conditions (such as ambient temperature) and, where applicable, the effectiveness of the NOx
aftertreatment system on NOx emissions are examined to address the research gaps in the literature.
The effects of ambient temperature on NOx emissions were found to be highly dependent on the
type of hybrid system of the buses. As ambient temperature decreased from 10 – 20°C to 0 – 10°C,
NOx emissions for parallel hybrid increased by 24.2%. However, the same reduction in ambient
temperature resulted in a 27.9% decrease in NOx emissions for the series hybrid. Ambient
temperature is currently not accounted for in the emission inventories.
A new dynamic emissions model, REVS (Road transport Emissions and Variance Simulator) is
proposed to address the variability in NOx emissions arising from different driving dynamics at
the same average speed. When compared to NOx emission factors measured by PEMS, REVS
provided an average reduction in the percentage discrepancy of 43 percentage points compared to
Computer Program to Calculate Emissions from Road Transport (COPERT), the EU standard
vehicle emissions calculator.
Version
Open Access
Date Issued
2023-06
Date Awarded
2024-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Stettler, Marc
Sponsor
Thailand
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)