Impact of hybrid/electric vehicles on urban air pollution

Lead Research Organisation: Imperial College London
Department Name: School of Public Health


Analytical and Environmental Sciences


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
NE/S013342/1 30/09/2018 30/06/2020
2125864 Studentship NE/S013342/1 01/11/2018 31/10/2022 William Hicks
Description 1. Improved Research methods: "CO2 dilution approach". The CO2 dilution approach is a novel technique to develop real-world road traffic emission factors. This work has utilised highly time-resolved atmospheric measurements of particulate matter mass, composition, and CO2 at a roadside and background location over a 12 month period. Using hourly traffic data, and fleet average CO2 emission factors, the CO2 Dilution approach enabled us to determine fleet average PM10/2.5/non-exhaust emission factors. These emission factors have a higher degree of certainty than previously developed real-world non-exhaust emission estimates which used a similar approach, albeit with NOx as the dilution gas and at a lower time resolution. Indeed, sensitivity tests have shown that CO2 emission factors have lower uncertainty than NOx emission factors and are less susceptible to variability in vehicle age/technology, ambient temperature, and engine loads, all of which have been demonstrated to cause discrepancies in real-world NOx emissions.

2. Significant new knowledge generated: Based on the highly-time resolved atmospheric measurement campaign and the CO2 dilution approach, the effect of lockdown on PM non-exhaust emissions was quantified. Lockdown saw a 32% reduction in traffic volume and a 15% increase in average speed on Marylebone Road, which resulted in lower PM10 and PM2.5 traffic increments and brake wear concentrations but similar tyre and resuspension concentrations. Brake wear was found to be the highest average non-exhaust emission source. In addition, the results indicate that non-exhaust emission factors were dependent upon speed and road surface wetness conditions.

Further details of the methods and results are presented in: Quantification of Non-Exhaust Particulate Matter Traffic Emissions and the Impact of COVID-19 Lockdown at London Marylebone Road.

Moreover, additional key findings are anticipated as a result of the work funded through this award due to the upcoming national measurement campaigns and statistical modelling of internal combustion / electric vehicle data.
Exploitation Route As this work is ongoing, further outcomes of this funding are anticipated as part of my PhD. For example, we are planning on undertaking roadside chemical composition measurements in Birmingham and Manchester (using a portable monitoring station) in Summer 2021. Using the CO2 dilution approach, this should enable us to determine nationally applicable non-exhaust emission factors. The impact of electrification on brake wear emission factors (e.g. due to regenerative braking) will also be quantified using the Bosch simulation data, to enable future projections in pollutant emission inventories.
Sectors Environment

Description Met with the Environment Minister Jo Churchill MP at Imperial's air quality monitoring site at London Marylebone Road on Clean Air Day
Geographic Reach National 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Description RBK Citizens' Assembly on Air Quality
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Participation in a guidance/advisory committee
Impact My role on the RBK Citizens' Assembly on Air Quality was to advise / oversee the citizens' assembly's plans, and ensure that evidence and materials relating to air quality were accurate, balanced and unbiased. The assembly brought together residents from the Royal Borough of Kingston upon Thames to develop recommendations on how to collectively improve air quality in the borough. The citizens' assembly heard a range of evidence relating to the impact of air pollution and different possible solutions for tackling it. Assembly members developed recommendations / actions, from which a report was presented to the Environment and Sustainable Transport committee of the Royal Borough of Kingston Council.
Description Robert Bosch Limited 
Organisation Bosch Group
Country Global 
Sector Private 
PI Contribution Bosch is the industrial CASE partner in my PhD studentship. We have provided our air pollution expertise, intellectual input and data analysis skills to this collaboration. For example, we have analysed brake data (using statistical / machine learning methods) which has been supplied by Bosch. We have also engaged in regular updates to inform progress of the study, explaining monitoring and modelling approaches, and informing our results etc..
Collaborator Contribution Bosch has supplied us with information, datasets and expertise, in particular relating to brake engineering. For example, Bosch has provided friction brake chemical composition data, laboratory dynamometer emissions data, and ICE / regenerative brake simulation data. These datasets are important contributions to the PhD to enable us to quantify the impact of electrification on brake wear emissions.
Impact N/A
Start Year 2018
Description Kingston Upon Thames Air Quality Citizens' Assembly 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact The RBK Citizens' Assembly was a group of 38 citizens broadly reflecting the population from the Royal Borough of Kingston upon Thames who came together over two weekends to consider how to improve air quality in the borough. I was a member of an independent advisory group (details on Section 1.2 of the attached URL), tasked with providing advice and oversight to ensure the citizens' assembly's plans, evidence and materials were accurate, balanced and unbiased. Following the citizens' assembly, a policy report was presented to RBK Council based on the findings of the assembly.
Year(s) Of Engagement Activity 2019