Vehicle dynamics and personal exposure to black carbon in the vicinity of at-grade pedestrian

303 Pages·2014·8.14 MB·English

Vehicle dynamics and personal exposure to black carbon
in the vicinity of at-grade pedestrian infrastructure

David Williams
October 2014

Submitted in part fulfilment of the requirements for the degree of
Doctor of Philosophy of Imperial College London

Centre for Transport Studies
Department of Civil and Environmental Engineering
Imperial College London
Declaration

Various measurement campaigns detailed within this thesis required practical assistance
from other researchers. All experimental designs, data processing, analyses and
interpretation are my own work.

I hereby certify that I have personally carried out all research detailed in this thesis, except
where otherwise stated.

David Williams
October 2014

Copyright Declaration

The copyright of this thesis rests with the author and is made available under a Creative
Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy,
distribute or transmit the thesis on the condition that they attribute it, that they do not use it
for commercial purposes and that they do not alter, transform or build upon it. For any reuse

or redistribution, researchers must make clear to others the licence terms of this work.
Page 2 of 303
Abstract

Urban areas are often subject to traffic-induced poor air quality. Variability in vehicle
operating behaviours’ at traffic management infrastructure leads to increased emission rates
of pollutant species harmful to health. Where these locations are also sites of pedestrian
activity, exposure to pollution is increased. This thesis demonstrates this mechanism through
measurement of vehicle dynamics and emissions modelling, with tailpipe emissions found to
be at least 20% greater when the vehicle is delayed due to mid-link crossings.

As it has no non-combustion sources, black carbon (BC) is a useful proxy for traffic related
emissions. Previous research into air quality at traffic management infrastructure has been of
an insufficient scale to identify the variability in pollutant concentration and exposure. This
thesis addresses this gap through an investigation into BC concentration and exposure at
traffic management infrastructure, demonstrating that fixed monitors over coarse temporal
and spatial scales are inadequate for assessing BC concentration and exposure, and finding
that public health and transport professionals are ill-equipped to make recommendations for
improvements on the basis of current data and understanding.

To provide data suitable for an assessment at the micro-scale, a measurement framework is
specified for the use of micro-aethalometers in urban areas. This addresses problems of
signal noise, aerosol loading and consistency where other studies have not, enabling
measurement of BC concentration at higher temporal resolution (5-second) than previously.
Micro-aethalometers are deployed at signalised intersections in London and Glasgow (UK).
The variability in BC is identified, with median concentration up to 130% greater at pedestrian
waiting locations across the intersection. In high traffic flow environments, the periodicity of
peak concentration episodes is found to relate to traffic control cycles. High-resolution data
are applied to pedestrian exposure studies, with in-transit exposure to BC varying by more
than ten times as a result of activity patterns.
Page 3 of 303
Dedication

This thesis is dedicated in loving memory to my mum, Margaret Williams.

Page 4 of 303
Acknowledgements

First and foremost, thanks are due to my supervisors, Dr Robin North, Professor Washington
Ochieng and Professor John Polak. Robin especially has been the source of much guidance,
support, opportunity and debate. My PhD experience would no doubt have been vastly
different without him. Thanks to Jackie Sime and Fionnuala Donovan, who expertly ensure
that the Centre and Department run smoothly. I was supported by an Engineering Physical
Sciences Research Council grant throughout my studies, for which I am grateful.

The data collection conducted over the past four years would not have been possible without
generous loans of equipment, including that from Dr John Gulliver of Imperial College
London, Jim Mills of Air Monitors Ltd and Martine Van Poppel and colleagues at Vito,
Belgium. I am also indebted to many CTS students and colleagues for their assistance in
collecting data at various times. Thanks particularly to Aravinth Thiyagarajah, with whom I
have collaborated on a great many and varied things over the past three years.

My time at Imperial was made more enjoyable by the people I met – Shane, Ara, Michael
and George to name but a few. Thanks for all the time spent in the SCR, the Holland Club
(RIP) and on the squash court. It’s also been a great experience getting to know and working
with lots of people in 610, TEA, CTS and Civil – I wish everyone the best in their future
endeavours.

Finally, thanks to my parents, siblings and friends for their encouragement and support over
many, many years. Special thanks to Em, provider of much food and coffee, and to my dad,
Barrie Williams, who always took the time to explain things to me.
Page 5 of 303
Contents
Declaration ........................................................................................................................... 2
Abstract ............................................................................................................................... 3
Dedication ............................................................................................................................ 4
Acknowledgements ............................................................................................................. 5
Contents............................................................................................................................... 6
List of tables .......................................................................................................................10
List of figures .....................................................................................................................12
Glossary ..............................................................................................................................17
1 Introduction ..........................................................................................................19
1.1 Environmental impacts of road transport ................................................................20
1.1.1 Greenhouse gas emissions ....................................................................................21
1.1.2 Local air quality ......................................................................................................22
1.1.3 Black carbon ..........................................................................................................23
1.2 Human exposure to pollution in urban areas ..........................................................23
1.2.1 Vehicle emission and air pollution hotspots ............................................................23
1.2.2 Activity and exposure hotspots ...............................................................................24
1.3 Current research issues .........................................................................................24
1.3.1 Traffic management and vehicle emissions ............................................................24
1.3.2 Local variability in air quality and personal exposure to pollution ............................25
1.3.3 Black carbon measurement techniques ..................................................................26
1.4 Research aims and objectives ................................................................................26
1.5 Thesis structure ......................................................................................................27
2 Traffic management and vehicle emissions .......................................................29
2.1 Formation of pollutant emissions ............................................................................29
2.1.1 Vehicle power requirements ...................................................................................29
2.1.2 Formation of typical pollutant species .....................................................................32
2.1.3 Particulate matter and black carbon .......................................................................33
2.1.4 Summary: formation of pollutant emissions ............................................................35
2.2 Fleet composition ...................................................................................................36
2.2.1 Fuel type ................................................................................................................36
2.2.2 Vehicle type ...........................................................................................................38
2.2.3 Vehicle age and technology ...................................................................................39
2.2.4 Summary: fleet composition ...................................................................................42
2.3 Traffic engineering and control (TEC) .....................................................................42
2.3.1 Urban intersections ................................................................................................43
2.3.2 Traffic signals .........................................................................................................44
2.3.3 Pedestrian facilities ................................................................................................46
2.3.4 Environmental impacts of interrupting traffic flow ....................................................47
Page 6 of 303
2.3.5 Summary: traffic engineering and control ...............................................................48
2.4 Approaches to reducing vehicle emissions .............................................................49
2.5 Existing research on the influence of TEC ..............................................................50
2.5.1 General influence of traffic engineering ..................................................................50
2.5.2 Research specific to traffic control ..........................................................................51
2.5.3 Critical review of relevant literature .........................................................................53
2.6 Summary: traffic management and vehicle emissions ............................................54
3 Traffic state, vehicle dynamics and emissions in the vicinity of at-grade
pedestrian infrastructure ...................................................................................................55
3.1 Background ............................................................................................................55
3.2 Pedestrian infrastructure in urban areas .................................................................56
3.2.1 Crossing grade and position ...................................................................................57
3.2.2 At-junction facilities ................................................................................................57
3.2.3 Mid-link facilities .....................................................................................................58
3.2.4 Summary: pedestrian infrastructure ........................................................................60
3.3 Experimental design ...............................................................................................60
3.3.1 Aims .......................................................................................................................61
3.3.2 General methodology .............................................................................................62
3.3.3 Measurement requirements ....................................................................................63
3.3.4 Site selection ..........................................................................................................65
3.3.5 Data collection procedure .......................................................................................67
3.4 Data processing .....................................................................................................68
3.4.1 Geographical definition ...........................................................................................68
3.4.2 Data availability ......................................................................................................71
3.4.3 Identifying delay .....................................................................................................72
3.5 Traffic characteristics .............................................................................................75
3.5.1 Vehicle delay ..........................................................................................................75
3.5.2 Acceleration noise ..................................................................................................79
3.6 Vehicle dynamics ...................................................................................................83
3.6.1 Candidate parameters ............................................................................................83
3.6.2 Observed distributions ............................................................................................85
3.7 Emission modelling ................................................................................................89
3.7.1 Background ............................................................................................................89
3.7.2 Analysis of Instantaneous Road Emissions (AIRE) ................................................91
3.7.3 Modelled emissions results ....................................................................................92
3.8 Implications for air quality and exposure ............................................................... 100
3.9 Summary: traffic state, vehicle dynamics and emissions ...................................... 103
4 Urban air quality, black carbon and pedestrian exposure to pollution .......... 106
4.1 Introduction to black carbon ................................................................................. 106
4.1.1 Sources ................................................................................................................ 108
4.1.2 Environmental impacts ......................................................................................... 108
4.1.3 Health impacts ..................................................................................................... 109
4.2 Black carbon management issues ........................................................................ 110
4.2.1 Legislative approaches ......................................................................................... 111
Page 7 of 303
4.2.2 Limitations ............................................................................................................ 112
4.2.3 Reporting of black carbon .................................................................................... 113
4.3 Assessing exposure to black carbon pollution ...................................................... 113
4.3.1 Framework for analysis ........................................................................................ 115
4.3.2 Assessing concentration ...................................................................................... 116
4.3.3 Studies of pollution variability ............................................................................... 117
4.3.4 Studies of exposure to black carbon and fine particulates .................................... 119
4.4 Summary: urban air quality, black carbon and pedestrian exposure to pollution ... 122
5 Measurement of black carbon ........................................................................... 124
5.1 Introduction to optical measurement of black carbon ............................................ 124
5.2 Aethalometer principles of operation .................................................................... 128
5.3 Micro-aethalometer use and issues ...................................................................... 131
5.3.1 Operational issues and post-processing techniques ............................................. 131
5.3.2 Micro-aethalometer use in urban pollution studies ................................................ 135
5.3.3 Summary .............................................................................................................. 137
5.4 Data characterisation and error identification ....................................................... 138
5.4.1 Equipment ............................................................................................................ 138
5.4.2 Initial data collection ............................................................................................. 139
5.4.3 Procedure ............................................................................................................ 141
5.4.4 Descriptive statistics ............................................................................................. 142
5.4.5 Time-series data .................................................................................................. 146
5.4.6 Time-base comparison ......................................................................................... 151
5.4.7 BC data summary ................................................................................................ 152
5.5 ONA performance ................................................................................................ 153
5.5.1 High-level performance ........................................................................................ 153
5.5.2 ATN reporting ....................................................................................................... 155
5.5.3 Summary of ONA performance ............................................................................ 159
5.6 Aerosol loading .................................................................................................... 160
5.6.1 Magnitude of loading effects ................................................................................. 160
5.6.2 Determining the impact of aerosol loading ............................................................ 162
5.6.3 Instrument specific loading effects ........................................................................ 165
5.6.4 Summary of aerosol loading effects ..................................................................... 167
5.7 Measurement consistency .................................................................................... 168
5.7.1 Sensor co-location ............................................................................................... 168
5.7.2 Initial results ......................................................................................................... 169
5.7.3 Correlation between units ..................................................................................... 174
5.7.4 Data smoothing .................................................................................................... 176
5.8 Summary: measurement of black carbon ............................................................. 178
6 Black carbon concentration at urban intersections ........................................ 180
6.1 Experimental aims and methods .......................................................................... 180
6.1.1 Aims ..................................................................................................................... 180
6.1.2 General approach ................................................................................................ 181
6.1.3 Micro-aethalometer deployment ........................................................................... 185
6.2 Byres Road .......................................................................................................... 187
Page 8 of 303
6.2.1 Site description ..................................................................................................... 187
6.2.2 Instrument deployment ......................................................................................... 190
6.2.3 Background data .................................................................................................. 192
6.2.4 Initial results ......................................................................................................... 193
6.2.5 Explanatory variables ........................................................................................... 198
6.2.6 Identifying peak events ......................................................................................... 201
6.2.7 Periodicity ............................................................................................................ 204
6.2.8 Location interdependence .................................................................................... 206
6.2.9 Byres Road summary ........................................................................................... 210
6.3 Cromwell Road ..................................................................................................... 211
6.3.1 Site description ..................................................................................................... 211
6.3.2 Background data .................................................................................................. 213
6.3.3 Instrument deployment ......................................................................................... 214
6.3.4 Results ................................................................................................................. 215
6.4 Site comparison ................................................................................................... 222
6.4.1 Similarities ............................................................................................................ 222
6.4.2 Relative magnitude and peak event occurrence ................................................... 222
6.4.3 Discussion of mechanisms responsible ................................................................ 227
6.5 Local meteorological impacts ............................................................................... 231
6.5.1 Approach .............................................................................................................. 231
6.5.2 Results ................................................................................................................. 234
6.6 Summary: black carbon concentration.................................................................. 238
7 Pedestrian exposure to black carbon ............................................................... 240
7.1 Probabilistic examination of BC concentration and exposure ............................... 240
7.1.1 Statistical distributions for air pollution .................................................................. 241
7.1.2 Distribution fitting and goodness-of-fit .................................................................. 242
7.1.3 Data ..................................................................................................................... 244
7.1.4 Results ................................................................................................................. 246
7.1.5 Additional model forms ......................................................................................... 249
7.1.6 Applications .......................................................................................................... 254
7.2 Exposure as a function of traffic control state ....................................................... 255
7.2.1 Determination of traffic control state ..................................................................... 255
7.2.2 Results ................................................................................................................. 257
7.2.3 Pedestrian crossing compliance ........................................................................... 258
7.2.4 Implications for pedestrian exposure and traffic management .............................. 261
7.3 In-transit pedestrian exposure .............................................................................. 264
7.3.1 Exposure indices .................................................................................................. 264
7.3.2 Variability in pedestrian exposure ......................................................................... 267
7.3.3 In-transit exposure results .................................................................................... 269
7.4 Summary: pedestrian exposure to black carbon ................................................... 272
8 Conclusions and further work ........................................................................... 274
8.1 Research objectives and conclusions ................................................................... 274
8.1.1 Objective 1: Traffic infrastructure induced emissions ............................................ 275
8.1.2 Objective 2: Measurement of black carbon ........................................................... 276
Page 9 of 303
8.1.3 Objective 3: Variability of black carbon ................................................................. 278
8.1.4 Objective 4: Pedestrian exposure ......................................................................... 280
8.2 Further research ................................................................................................... 281
8.2.1 Limitations of this work ......................................................................................... 281
8.2.2 Transport, environment and health policy ............................................................. 282
8.2.3 Vehicle dynamics and emissions formation .......................................................... 283
8.2.4 Measurement of black carbon .............................................................................. 283
8.2.5 Variability in black carbon concentration ............................................................... 284
8.2.6 Exposure to black carbon ..................................................................................... 285
References ........................................................................................................................ 286
Appendices ....................................................................................................................... 297
Appendix I: European emission standards for passenger cars ........................................... 297
Appendix II: Example GPS output ...................................................................................... 298
Appendix III: GPS trajectory/AIRE conversion processing script ......................................... 299
Appendix IV: Micro-aethalometer output data ..................................................................... 302
Appendix V: Summary of permission for third party copyright works ................................... 303

List of tables

Table 1-1: Passenger transport by mode, 2011 (DfT, 2012a). ..............................................20
Table 2-1: Hot exhaust emission factors for the UK vehicle fleet (Defra, 2013). ...................36
Table 2-2: European emission standards for new diesel passenger cars. ............................40
Table 2-3: Types of traffic intersection (from Slinn et al, 2005). ............................................43
Table 2-4: Advantages and disadvantages of traffic control (from Rogers, 2008). ................45
Table 2-5: Definitions of vehicle operating mode (from Frey et al, 2001). .............................47
Table 3-1: Different options for accommodating pedestrians at signalised intersections. ......58
Table 3-2: Mid-link options for accommodating pedestrians. ................................................59
Table 3-3: Variables controlled, or mitigated for, through experimental design. ....................62
Table 3-4: RNP (required navigation performance) parameters (from Ochieng et al, 1999). .64
Table 3-5: Type, location and description of pedestrian crossings included in the study. ......66
Table 3-6: Observed distance and speed by site. .................................................................74
Table 3-7: Mann-Whitney-Wilcoxon test statistics. ................................................................82
Table 3-8: Models for estimating tailpipe emissions (from Barlow and Boulter, 2009). ..........90
Table 3-9: Descriptive statistics for the entire sample, zebra and signal-controlled portions. 94
Table 3-10: Crossing 12 modelled emission results for selected observations of traffic,
pedestrian crossing and no delay. ........................................................................................97
Table 3-11: Crossing 9 emission results for selected observations of traffic, pedestrian
crossing and no delay...........................................................................................................99
Page 10 of 303