Characterisation of FAGE apparatus for HOx detection and application in an environmental chamber

259 Pages·2014·8.6 MB·English

Characterisation of FAGE apparatus for HOx
detection and application in an environmental
chamber

Frank Alexander Frederick Winiberg

Submitted in accordance with the requirements for the degree of Doctor of Philosophy

The University of Leeds
School of Chemistry

The candidate confirms that the work submitted is his own and that appropriate credit
has been given where reference has been made to work of others.
This copy has been supplied on the understanding that it is copyright material and that
no quotation from the thesis may be published without proper acknowledgement.
© 2014 The University of Leeds and Frank Winiberg

Acknowledgments
So this is where I’m supposed to write something nice about people…

Well… I tried.
Hello. I’m sat writing this with a large Ardmore whiskey at 1.45 am on the day before
I’m going to submit, so hopefully by the end, things will still be coherent. I’ve been to a
lot of cool places and met a load of interesting people along the way. I’m sure in the
rush I’ll forget someone. If it’s you, then there’s a blank page before this one
First and foremost, Paul and Dwayne: thank you for offering me the opportunity to stay
on after my masters. I’ve had a load of fun within the groups and learnt a lot along the
way. Hopefully I’ve not been too much of a burden.
Shona: You helped field far too many of my stupid questions in my first couple of
years. Thanks for being my personal organiser and providing me with helpful criticism,
like “yuk” and “eurgh”. I didn’t flounce out of the room once whilst writing up. Honest.
Jess: I honestly can’t believe how patient you’ve been. I think I’ve been living in work
and on my laptop for the last two years, and for some reason you’ve understood, let me
get on with it and tried to offer me help. You’re clearly as crazy as I originally thought.
Mark and Trev: Cheers for the help in the lab. A lot of time was lost on my endless
questions about lasers and FAGE, I’m sure.
Pete: Cheers for giving me a place to live right at the start of my PhD dude. The North
View Hostel was a fun (if cold) place to live. Oh, and the endless Blackadder quotes
will never get old, despite what Jenny thinks. Maaaaah!
Mum and Dad (a.k.a Gut Bucket): I did it! All that effort you put in to raising the
perfect son finally paid off… Yes I am getting a job now (hopefully). No I’m not
moving home. Yes I realise so-and-so left uni and dossed around for a year and sponged
of his/her parents. Please stop asking. Thanks for being so understanding this last year.
Basement guys: Thanks for making that rather Vitamin-D-deficient office a fun place to
work. The random conversations and endless cups of tea and coffee have helped me
develop a healthy caffeine habit. I think we definitely have more fun than that horrible
Dainton lot upstairs.
Dainton people: Thanks for letting me get away from those annoying basement
dwellers. They’re so chatty and force me to have endless cups of tea. You guys were
awesome. Pub trips and late night records/arguments/arguments about records. Fun
times. The motivational dances were particularly helpful in the final weeks.
Abstract
The hydroxyl radical, OH, and the hydroperoxy radical, HO (known collectively as
2
HOx), play a key role in tropospheric chemistry and are intricately related to chemical
cycles that control the concentration of greenhouse gases and have important
implications for air quality. Through accurate measurements of these two important
radicals, and thorough investigation of the chemical mechanisms that control their
formation and removal, we can develop a better understanding of atmosphere.
Simulation chambers offer the unique ability to study these processes under
atmospherically relevant conditions, using a wide variety of instrumentation to probe
many different species. The Highly Instrumented Reactor for Atmospheric Chemistry
(HIRAC) is a stainless steel chamber based at the University of Leeds and was
previously designed to operate over a range of temperatures and pressures. HIRAC was
implemented to validate important oxidation mechanisms of volatile organic
compounds, furthering mechanism databases, such as the Master Chemical Mechanism
(MCM).
This thesis concentrates on the continued development of a dedicated HOx radical
detection instrument, based on laser induced fluorescence spectroscopy at low pressure
(fluorescence assay by gas expansion (FAGE)), for use in an atmospheric simulation
chamber. In the field, FAGE instruments are designed to operate on board aircraft,
which subject the instrument to a range of external operating pressures. Thorough
characterisation and calibration of the FAGE instrument was performed using
traditional methods, accounting for several factors known to affect instrument
sensitivity. This calibration procedure was successfully validated using two newly
developed calibration methods for OH and HO , which take advantage of the HIRAC
2
chamber and its ability to operate over a range of temperatures and pressures.
After thorough calibration, the instrument was implemented in the investigation of
direct OH radical production from the reaction of HO with acetylperoxy radicals in the
2
HIRAC chamber. Reactions of RO radicals with HO have previously been thought to
2 2
be a radical sink in atmospherically pristine environments (i.e., low NOx). However,
more recently, higher than anticipated concentrations of OH have been observed in
areas where biogenic loadings are high. Recycling of OH from reactions of RO with
2
HO could provide part of the current mechanism shortfall. Acetyl peroxy radicals are
2
of particular importance as they are formed directly from the oxidation of MVK, a
major product of isoprene oxidation. Reported here is the first study sensitive to
products from all three branching pathways of the reaction.
Table of Contents
Table of Contents .......................................................................................................... vii
List of Figures ................................................................................................................. xi
Chapter 1. The tropospheric chemistry of OH and HO radicals ...................................... 1
2
1.1 Motivation and project aims ............................................................................... 2
1.2 Tropospheric chemistry of the hydroxyl radical: an outline .............................. 5
1.3 Comparison of field work with comprehensive reaction mechanisms ............... 7
1.4 HOx chemistry in areas with high biogenic VOC emissions ........................... 10
1.5 Mechanism of the OH initiated oxidation of isoprene ..................................... 13
1.6 HOx radical measurement techniques .............................................................. 15
1.6.1 Calibration methods .................................................................................. 18
1.6.2 HOx measurement interferences ............................................................... 20
1.6.3 Validation through intercomparison ......................................................... 22
1.7 References ........................................................................................................ 24
Chapter 2. The Highly Instrumented Reactor for Atmospheric Chemistry .................... 33
2.1 Introduction ...................................................................................................... 34
2.2 The HIRAC Chamber ....................................................................................... 38
2.2.1 Temperature control .................................................................................. 40
2.2.2 Gas handling and sample preparation ....................................................... 41
2.2.3 Data acquisition ......................................................................................... 42
2.2.4 Artificial light sources ............................................................................... 42
2.3 Instrumentation ................................................................................................. 48
2.3.1 FTIR .......................................................................................................... 48
2.3.2 GC-FID ..................................................................................................... 50
2.3.3 Commercial trace-level gas analysers ....................................................... 53
2.3.4 Dilution compensation system .................................................................. 53
vii
2.4 References ........................................................................................................ 55
Chapter 3. Quantitative FTIR Analysis Techniques ....................................................... 59
3.1 Introduction ...................................................................................................... 60
3.1.1 Peak area/height analysis .......................................................................... 66
3.1.2 Spectral subtraction ................................................................................... 67
3.1.3 Classic Least Squares (CLS) ..................................................................... 69
3.1.4 Inverse Least Squares (ILS): the Multiple Linear Regression method
(MLR) 71
3.1.5 PCA and PLS ............................................................................................ 72
3.1.6 Spectral synthesis for quantitative analysis .............................................. 72
3.2 Reference Spectra - Guidelines ........................................................................ 73
3.3 Software Development ..................................................................................... 74
3.3.1 Non-linear least-squares fitting algorithm ................................................ 78
3.4 Results and discussion ...................................................................................... 80
3.4.1 Reaction of Cl atoms with butane isomers................................................ 80
3.4.2 Application to HO + CH C(O)O ............................................................ 83
2 3 2
3.5 Uncertainty analysis ......................................................................................... 86
3.5.1 Manual subtraction .................................................................................... 86
3.5.2 Quant2 ....................................................................................................... 86
3.6 Conclusions and further work .......................................................................... 88
3.7 References ........................................................................................................ 90
Chapter 4. HOx instrumentation ..................................................................................... 93
4.1 Introduction ...................................................................................................... 94
4.2 The FAGE technique ........................................................................................ 95
4.3 FAGE instrumentation ..................................................................................... 97
4.4 FAGE instrument for HOx radical detection in the HIRAC chamber ........... 100
4.4.1 Laser systems and light delivery ............................................................. 103
viii
4.4.2 Reference cell .......................................................................................... 105
4.4.3 Data acquisition ....................................................................................... 105
4.5 Aircraft instrument ......................................................................................... 110
4.6 Summary ........................................................................................................ 112
4.7 References ...................................................................................................... 114
Chapter 5. FAGE Instrument Calibration and Characterisation ................................... 119
5.1 Introduction .................................................................................................... 120
5.2 Water vapour photolysis ................................................................................. 122
5.2.1 Experimental ........................................................................................... 123
5.2.2 Results ..................................................................................................... 126
5.2.3 Uncertainty analysis ................................................................................ 138
5.2.4 Limit of Detection ................................................................................... 139
5.3 Calibration source characterization, F .................................................. 140
184.9nm
5.3.1 N O actinometry...................................................................................... 141
2
5.3.2 O actinometry ........................................................................................ 144
2
5.3.3 Uncertainty analysis ................................................................................ 146
5.3.4 O cross section ....................................................................................... 147
2
5.4 RO interference in HO measurements ......................................................... 152
2 2
5.5 Conclusions and future work .......................................................................... 154
5.6 References ...................................................................................................... 156
Chapter 6. Alternative FAGE calibration methods ....................................................... 161
6.1 Introduction .................................................................................................... 162
6.2 Experimental .................................................................................................. 164
6.2.1 General HIRAC preparation and instrumentation................................... 164
6.2.2 Hydrocarbon decay calibration ............................................................... 165
6.2.3 Formaldehyde photolysis ........................................................................ 170
6.3 Data analysis procedure .................................................................................. 171
ix
6.3.1 Hydrocarbon decay ................................................................................. 171
6.3.2 Formaldehyde photolysis ........................................................................ 175
6.4 Results and discussion .................................................................................... 178
6.4.1 Hydrocarbon decay ................................................................................. 178
6.4.2 Formaldehyde photolysis calibration ...................................................... 181
6.5 Uncertainties ................................................................................................... 184
6.5.1 Hydrocarbon Decay Calibration ............................................................. 184
6.5.2 Formaldehyde photolysis calibration ...................................................... 185
6.6 Conclusions and further work ........................................................................ 186
6.7 References ...................................................................................................... 188
Chapter 7. OH yield measurements from the reaction of acetylperoxy and HO radicals
2
....................................................................................................................................... 191
7.1 Introduction .................................................................................................... 192
R 7.4c ............................................................................................................................ 192
7.2 Experimental .................................................................................................. 196
7.2.1 Chamber and instrumentation ................................................................. 196
7.2.2 Chemicals, sample preparation and gas handling ................................... 197
7.2.3 Radical generation and experimental process ......................................... 197
7.2.4 Chemical model ...................................................................................... 199
7.3 Results and Discussion ................................................................................... 202
7.3.1 Reaction of C H O with HO ................................................................ 202
2 5 2 2
7.3.2 Reaction of CH C(O)O with HO .......................................................... 209
3 2 2
7.4 Comparison with literature data ..................................................................... 229
7.4.1 Branching ratios ...................................................................................... 229
7.5 Conclusions, atmospheric implications and further work .............................. 231
7.6 References ...................................................................................................... 233

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