The concentrations, behaviour and fate of polycyclic aromatic hydrocarbons

379 Pages·2015·6.4 MB·English

by  Ian James Keyte

The concentrations, behaviour and fate of polycyclic
aromatic hydrocarbons (PAHs) and their oxygenated
and nitrated derivatives in the urban atmosphere

by
Ian James Keyte

A thesis submitted to the University of Birmingham for the degree of
Doctor of Philosophy

Division of Environmental Health and Risk Management, School of
Geography, Earth and Environmental Sciences, University of
Birmingham, Edgbaston, B15 2TT, United Kingdom

December 2014
University of Birmingham Research Archive

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Abstract

Polycyclic aromatic hydrocarbons (PAHs) play an important role in urban air quality due to the toxic
and carcinogenic hazard they present. A class of pollutants receiving increasing interest from
researchers are oxygenated (OPAH) and nitrated (NPAH) derivative compounds. There is a need
for an improved understanding of the sources, concentrations, behaviour and fate of these
pollutants as they can pose a similar public health risk as PAHs and can enter the environment
both from primary combustion emissions and secondary formation from atmospheric reactions.
This study investigates the airborne concentrations of PAH, OPAH and NPAH compounds in U.K.
atmosphere at heavily trafficked and urban background sites. Sampling campaigns were
conducted to assess the spatial and temporal trends, primary and/or secondary sources, gas-
particle phase partitioning and atmospheric degradation of PAHs, NPAHs and OPAHs. Differences
in atmospheric concentrations between trafficked sites and the urban background site indicate a
variable influence of road traffic emissions between different PAH, OPAH and NPAH compounds.
Seasonal, diurnal and temporal patterns as well as positive matrix factorisation (PMF) source
apportionment provide evidence of the key influencing factors governing the concentrations of
PAHs, OPAHs and NPAHs in the urban atmosphere, in addition to the strength of road traffic
emissions. For example, specific non-traffic sources are identified at these sites including
combustion sources such as domestic and non-domestic wood combustion, and non-combustion
sources such as temperature-driven volatilisation from surfaces. Evidence for the occurrence of
PAH reactivity and atmospheric formation of NPAH and OPAH compounds between traffic and
background sites is also observed, with the relative rates of atmospheric degradation shown to
play a key role influencing the observed concentrations at these sites. It is also indicated that
emissions of NPAHs from road traffic relative to PAHs have increased substantially in the last 20
years, consistent with the increased proportion of diesel passenger vehicles in the U.K. traffic fleet.

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Acknowledgements

I would like firstly to say a huge thank you Professor Harrison. It was always going to take careful,
considered and wise supervision to guide someone as dense as me though a PhD. Thanks for
being up to the challenge. I would also be remiss if I didn’t say thanks to Mary for putting up with all
my stupid questions and sorting out things like infuriating international order requests and many
many other things.

In particular I need to thank Chris, whose guidance, support and infinite patience in the lab has
made this project possible. I literally could not have done it without him. I would also like to thank
Salim for being a friendly and reassuring presence in the frustrating and often miserable toil of lab
work and for being a good companion on our adventures in Munster and Oregon.

I am grateful to Gillian and Eimear for their help in the lab and especially to Richard and Jamie,
who have been amazingly helpful and kind and helped me avoid more than a few potential
disasters. I also need to thank Duick Young for his help with accessing Elms Cottage weather data
and the good folks at Amey for helping with the tunnel sampling,

To my great friends/co-conspirators for the last 4 years - Pallavi, Max, Barbara, Karima, Paul and
Anna - you are all truly insane and wonderful - in that order (especially you, Pallavi). There is no
way I could have made it through this without laughing so much with and/or at you (you again,
Pallavi). Lunchtime will never be as much fun without you. I also say thanks to all the members of
the 4th Floor Crew over the years, who it has been a pleasure to know.

Je dis un grand merci à Perrine for being so supportive and patient with me while I have been
working on this and for her important guidance on important complex technical issues like how to
use a computer.

But above all I want to thank my dad, who has always supported me and never given up on me
even during all the times I have given up on myself and even though I sometimes give him every
reason to. I am truly grateful. Cheers dad.

“Life is a ball of beauty that makes you want to just cry......then you die”. – Kurt Vile.
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Contents

Page No.
1. Introduction

1.1. Polycyclic aromatic hydrocarbons (PAHs), urban air quality and public health 1
1.1.1. Urban air quality and public health 1
1.1.2. The chemical and physical properties of PAHs, OPAHs and NPAHs 2
1.1.3. Policy issues 3

1.2. Sources of PAHs, OPAHs and NPAHs 8
1.2.1. Sources of PAHs 8
1.2.2. Sources of OPAHs and NPAHs 12
1.2.3. Emissions from road traffic 13

1.3. Health effects of PAHs, OPAHs and NPAHs 15
1.3.1. Exposure to PAHs 15
1.3.2. The metabolism and toxicity mechanism of PAHs, NPAHs and OPAHs 16
1.3.3. Heath effects of PAHs 17
1.3.4. The role of PAHs in the health effects of urban air 20
1.3.5. The role of atmospheric PAH reactions on toxic effects 23

1.4. Occurrence and behaviour of PAHs in the atmosphere 26
1.4.1. Occurrence in the environment 26
1.4.1.1. PAHs in the environment 26
1.4.1.2. OPAHs and NPAHs in the atmosphere 27
1.4.2. Gas-particle partitioning of PAH, OPAH and NPAH compounds 29
1.4.2.1. Phase partitioning of PAHs 29
1.4.2.2. Phase partitioning of OPAHs and NPAHs 31
1.4.3. Atmospheric transport of PAHs 32
1.4.4. Long-term concentration trends 33
1.4.5. Short term concentration variations 34
1.4.5.1. Seasonal patterns 34
1.4.5.2. Diurnal patterns 35
1.4.6. Ambient sampling of PAH in the U.K. atmosphere 36
1.4.6.1. PAH monitoring in the U.K. 36
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1.4.6.2. PAHs from road traffic 37

1.5. Fate of PAHs, OPAHs and NPAHs in the atmosphere 37
1.5.1 Wet and dry deposition of PAHs 38
1.5.2. Photolysis 39
1.5.2.1. Photolysis of PAHs 39
1.5.2.2. Photolysis of OPAH and NPAH 41
1.5.3 Atmospheric reactivity of PAHs 42
1.5.3.1. Gas-phase PAH reactions 43
1.5.3.2. Heterogeneous reactions 51
1.5.3.3. Evidence for PAH reactions in ambient air samples 55
1.5.4. Reactions of OPAH and NPAH 57
1.6. Project aims and objectives 58

2. Methodology 61

2.1 Sampling Procedure 61

2.1.1. Background 61
2.1.1.1. Overview 61
2.1.1.2. Particle-phase sampling 62
2.1.1.3. Gas-phase sampling 62
2.1.2. Sampling sites 64
2.1.3. Sampling campaigns 67
2.1.3.1. Campaign 1 : seasonal 24 hour sampling 67
2.1.3.2. Campaign 2 : diurnal sampling study 70
2.1.3.3. Campaign 3: Queensway Road Tunnel sampling study 71
2.1.4. Meteorological data 72
2.1.5. Inorganic gaseous pollutants 72
2.1.6. Quality control : the potential impact of sampling artefacts 73
2.1.6.1. Gas-phase vs. particle-phase artefacts 73
2.1.6.2. Chemical reactivity during sampling 73
2.1.6.3. Artefact sampling experiment 75

2.2. Sample extraction and clean-up 76
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2.2.1. Materials and chemicals 76
2.2.2. Sample preparation 76
2.2.3. Sample extraction 76
2.2.3.1. Extraction background 76
2.2.3.2. Extraction method 78
2.2.4. Clean-up 78
2.2.4.1. Clean-up background 78
2.2.4.2. Clean-up method 79
2.3. Sample analysis 81
2.3.1. Background and analytical development 81
2.3.2. Analysis method for PAHs : GC-MS in EI mode 82
2.3.3. Analysis for OPAH and NPAHs : GC-MS in NICI mode 83
2.4. Sample Quantification 86
2.4.1. Sample concentrations 86
2.4.2. Validating analytical method 92
2.4.2.1. Recoveries 92
2.4.2.2. Standard reference material analysis (SRM) 92
2.4.2.3. Sample blanks 93
2.4.2.4. Detection Limits 93

3. Concentrations, behaviour and fate of PAHs, OPAHs and NPAHs
in the ambient urban atmosphere 99

3.1. Measured concentrations of PAH, OPAH and NPAH 99
3.1.1 PAH and OPAH concentrations 99
3.1.2. NPAH concentrations 110
3.1.3. BROS/EROS ratio comparisons 111
3.1.4. Traffic increment 115
3.1.5. Annual BaP concentrations and the UK Air Quality Objective 118

3.2. Influencing factors governing observed concentrations 118

3.2.1. Inter-correlations of PAH, OPAH and NPAH concentrations 119
3.2.2. Correlations with inorganic air pollutants and meteorological parameters 123
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3.2.2.1. Correlations of PAH, OPAH and NPAH with TSP 123
3.2.2.2. Correlations of PAH, OPAH and NPAH with NOx 126
3.2.2.3. Correlations of PAH, OPAH and NPAH with O 127
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3.2.2.4. Temperature-dependence of PAH, OPAH and NPAH concentrations 127
3.2.2.5. Rainfall, Wind speed and wind direction 129

3.3. Seasonal variation in PAH, OPAH and NPAH levels 130
3.3.1. PAH seasonality 130
3.3.2. OPAH and NPAH seasonality 134
3.3.3. Factors influencing seasonal trends 137
3.3.3.1. Seasonal variation in source strength 137
3.3.3.2. Seasonality of atmospheric boundary layer height 138
3.3.3.3. Influence of volatilisation from surfaces 139
3.3.4. Seasonal trend in PAH reactivity 141
3.3.5. BROS/EROS ratio seasonality 142

3.4. Temporal trend of PAHs at BROS and EROS 145
3.4.1. Overview 145
3.4.2. Temporal trend in PAH and OPAH concentrations 148
3.4.3. Temporal trend in NPAH concentrations 153

4. Gas-particle partitioning, chemical reactivity and source apportionment of PAHs,
OPAHs and NPAHs, and the influence of sampling artefacts 155
4.1. Gas-particle partitioning of PAHs, OPAHs and NPAHs 155
4.1.1. Phase partitioning overview 155
4.1.1.1. Phase partitioning of PAHs 155
4.1.1.2. Phase partitioning of OPAH and NPAH 156

4.1.2. Physiochemical properties influencing partitioning 157
4.1.3. Seasonality in partitioning behaviour 171
4.1.4. Phase partitioning equilibrium behaviour 173

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4.2. Assessing the importance of PAH reactivity in the urban atmosphere 178
4.2.1. PAH degradation rates 178
4.2.2. 2NFlt / 1NPyr ratios 179
4.2.3. 2NFlt / 2NPyr ratios 181
4.2.4. Product to reactant ratios 184

4.3. Source apportionment of PAH, OPAH, NPAH compounds using 188
Positive Matrix Factorization (PMF)
4.3.1 Introduction 188
4.3.2. Method 191
4.3.3. Results 193
4.3.1. Overview 193
4.3.3.2. Model uncertainty and rotational freedom 193
4.3.3.3. Source contributions 196

4.4. Sampling artefact study 201
4.4.1. Method 201
4.4.1.1. Sampling 201
4.4.1.2. Analysis 202
4.4.1.3. PAH recovery 203
4.4.1.4. OPAH and NPAH formation 203
4.4.2. Results 203
4.4.2.1. Observed PAH losses 203
4.4.2.2. Conversion of PAH to OPAH or NPAH during sampling 210
4.4.3. Summary 215

5. Diurnal profiles of PAH, OPAH and NPAH 216
5.1. BROS and EROS diurnal profiles 216
5.2. NO -corrected diurnal profiles 225
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5.3. Assessing role of PAH degradation and reactive input of NPAH and OPAH 229
5.3.1. PAH degradation 229
5.3.2. 2NFlt/1NPyr and 2NFlt/2NPyr Ratios 230
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5.3.3. Reactant/Parent Ratios 232

6. Concentrations of PAHs, OPAHs and NPAHs in the Queensway Road Tunnel 235
6.1. Tunnel concentrations of PAHs, OPAHs and NPAHs 235
6.1.1. PAH and OPAH concentrations 235
6.1.2. NPAH concentrations 238
6.1.3. Comparison with other Tunnel studies 242
6.1.4. Gas-particle phase partitioning 246

6.2. Temporal trend in PAH and NPAH concentrations 250
6.2.1. Temporal trend of PAHs 250
6.2.2. The driving force behind emission changes 254
6.2.3. Temporal trend of NPAHs 255

6.3. Comparison of tunnel vs. ambient concentrations 258
6.3.1. Overview 258
6.3.2. Tunnel/EROS ratios of PAHs 259
6.3.3. Tunnel/EROS ratios of OPAHs 262
6.3.4. Tunnel/EROS ratios of NPAHs 263

7. Conclusion 267
7.1. Investigation summary 267
7.2. Recommendations for future work 270

References 272

Appendix 1 : Reaction kinetics data for gas phase and heterogeneous PAH reactions 305
Appendix 2 : Sampler calibration and total air flow calculation 320
Appendix 3 : PAH, OPAH and NPAH gas chromatograph peaks 323

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