Development and Deployment of an Airborne Gas Chromatography/Mass Spectrometer to ...

212 Pages·2017·12.23 MB·English

Development and Deployment of an Airborne Gas
Chromatography/Mass Spectrometer to Measure
Tropospheric Volatile Organic Compounds
Jamie Minaeian
PhD
University of York
Chemistry
September 2016
Abstract
Airborne Volatile Organic Compounds are present throughout the atmosphere in a wide
variety of species. An airborne Gas Chromatography/Mass Spectrometer was developed
to measure these compounds in places otherwise inaccessible for ground- or ship-based
instruments. The instrument was fitted to the UK FAAM BAe-146 Atmospheric Research
Aircraft, and deployed on a number of campaigns. By the end of the project, the in-
strument was capable of making measurements that compared extremely well to other
systems, meaning the proof of concept was successful. During the SAMBBA campaign,
vertical profiles of biogenic and anthropogenic species were determined from the ground,
up to 8000 m. These showed the extent to which different compounds (for example CO,
benzene) were able to escape the planetary boundary layer and enter the free troposphere.
Isoprene, however, with a much shorter lifetime of 0.5 hours, was primarily constrained to
the boundary layer. Additionally, an analysis of biomass burning emissions was compared
to those in literature. In particular the CO:VOC ratio was compared, with some species
exhibiting very close comparisons, and others showing very different ratios leading to the
conclusion that the CO:VOC ratio for some compounds is highly dependent on the species
of trees. Measurements from the CAST campaign determined the extent to which natu-
rally occurring halogenated species can travel from their source at the ocean surface, up
to the lower stratosphere, affecting ozone levels. A comparison was also conducted with
3 other aircraft systems, for which the GC/MS was in good agreement. Finally, flights
were conducted around the North Sea Oil and gas fields to determine background levels
of compounds, in case of further leaks from natural gas extraction. Whilst the GC/MS
could not identify specific plumes, calculations were performed to enhance the readings,
showing very different levels of benzene emitted, which was dependent on the rig type.
2
Contents
Abstract 2
List of figures 6
List of tables 16
Acknowledgements 19
Declaration 20
1 Introduction 21
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.1.1 Structure and Composition . . . . . . . . . . . . . . . . . . . . . . . 22
1.1.1.1 Hydroxyl Radical, OH . . . . . . . . . . . . . . . . . . . . . 24
1.1.1.2 Stratospheric Ozone . . . . . . . . . . . . . . . . . . . . . . 25
1.1.1.3 Tropospheric Ozone . . . . . . . . . . . . . . . . . . . . . . 26
1.1.2 Emissions of NMHCs. . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.1.3 Removal Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.1.3.1 Wet and Dry Deposition . . . . . . . . . . . . . . . . . . . 30
1.1.3.2 Chemical Removal Processes . . . . . . . . . . . . . . . . . 30
1.1.4 Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1.1.5 Measurement Platforms and Technique . . . . . . . . . . . . . . . . 33
1.1.5.1 Ground Based Sampling. . . . . . . . . . . . . . . . . . . . 33
1.1.5.2 VOC Trends . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1.1.5.3 Ship Based Sampling . . . . . . . . . . . . . . . . . . . . . 37
1.1.5.4 Aircraft Based Sampling . . . . . . . . . . . . . . . . . . . 37
1.1.6 Overview of Gas Chromatography . . . . . . . . . . . . . . . . . . . 39
3
Contents
1.1.6.1 Theoretical Plates and Chomatographic Resolution . . . . 39
1.1.6.2 Applications of GC in Atmospheric Measurements . . . . . 41
1.1.7 Thermal Desorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.1.8 Mass Spectrometer Theory and Applications . . . . . . . . . . . . . 42
1.1.8.1 Mass Spectrometer Theory . . . . . . . . . . . . . . . . . . 42
1.1.8.2 Ionisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
1.1.8.3 Mass Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 43
1.1.8.4 Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
1.1.9 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
1.1.9.1 FAAM BAe-146 . . . . . . . . . . . . . . . . . . . . . . . . 46
1.1.10 Thesis Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2 Experimental and Instrument Development 51
2.1 Experimental and Instrument Development . . . . . . . . . . . . . . . . . . 52
2.1.1 Instrument in its Initial State . . . . . . . . . . . . . . . . . . . . . . 53
2.1.1.1 Cylinders and Calibrations . . . . . . . . . . . . . . . . . . 53
2.1.1.2 Sample Pressurisation/Pump Tray . . . . . . . . . . . . . 53
2.1.1.3 Power Distribution Box (PDB) . . . . . . . . . . . . . . . . 54
2.1.1.4 Flow Control Box (FCB) . . . . . . . . . . . . . . . . . . . 54
2.1.1.5 Thermal Desorption Unit (TDU) . . . . . . . . . . . . . . . 56
2.1.1.6 Gas Chromatograph (GC) . . . . . . . . . . . . . . . . . . 58
2.1.1.7 Mass Spectrometer (MS) . . . . . . . . . . . . . . . . . . . 59
2.1.2 Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.1.2.1 Cold-finger water removal . . . . . . . . . . . . . . . . . . . 60
2.1.2.2 On-column refocusing . . . . . . . . . . . . . . . . . . . . . 61
2.1.2.3 Nafion bundle drier . . . . . . . . . . . . . . . . . . . . . . 63
2.1.2.4 Stirling cooler water removal and CO heater . . . . . . . . 64
2
2.1.2.5 Arduino Microcontroller . . . . . . . . . . . . . . . . . . . . 71
2.1.3 Instrument Performance and Reproducibility . . . . . . . . . . . . . 72
2.1.3.1 Standard Operation Procedure . . . . . . . . . . . . . . . . 72
2.1.3.2 Calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2.1.4 Instrumental Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
2.1.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4
Contents
3 The Vertical and Spatial Distribution of Isoprene over Amazonia 82
3.1 The vertical and Spatial distribution of Isoprene over Amazonia . . . . . . . 83
3.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.1.2 Experimental and Flight Planning . . . . . . . . . . . . . . . . . . . 86
3.1.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.1.4 Methyl Vinyl Ketone and Methacrolein Analysis . . . . . . . . . . . 99
3.1.5 CO:VOC Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3.1.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4 Coordinated Airborne Studies in the Tropics (CAST) Project 120
4.1 Coordinated Airborne Studies in the Tropics (CAST) Project . . . . . . . 121
4.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.1.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.1.1.2 Motivations for this Study . . . . . . . . . . . . . . . . . . 122
4.1.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.1.2.1 Flight Planning . . . . . . . . . . . . . . . . . . . . . . . . 125
4.1.2.2 Science Payload . . . . . . . . . . . . . . . . . . . . . . . . 127
4.1.2.3 Mid-campaign Modifications . . . . . . . . . . . . . . . . . 131
4.1.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.1.3.1 Calibrations and Comparisons with other aircraft . . . . . 131
4.1.3.2 Back Trajectories . . . . . . . . . . . . . . . . . . . . . . . 141
4.1.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
5 Investigations into North Sea Oil and Gas Fields 151
5.1 Investigations into North Sea Oil and Gas Fields . . . . . . . . . . . . . . . 152
5.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
5.1.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
5.1.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
5.1.3.1 Survey Flights . . . . . . . . . . . . . . . . . . . . . . . . . 159
5.1.3.2 Southern Sector Flights . . . . . . . . . . . . . . . . . . . . 159
5.1.3.3 B913 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5.1.3.4 B918 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
5.1.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
5.1.5 Comparison with Background Levels over the Arctic . . . . . . . . . 167
5
Contents
5.1.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
6 Conclusions 172
6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
6.1.1 Further work and Final Thoughts. . . . . . . . . . . . . . . . . . . . 175
A Appendix A: Arduino Code 177
B Aircraft Standard Operating Procedures 185
Abbreviations 194
References 196
6
List of Figures
1.1 Average temperature and pressure variation with altitude at mid-latitudes,
showing distinct layers of the atmosphere . . . . . . . . . . . . . . . . . . . 22
1.2 Ozone, NO and RH cycling in the troposphere. Note that sunlight must
x
be present for these reactions to occur . . . . . . . . . . . . . . . . . . . . . 27
1.3 NAEI emissions map for the UK for 2014. The map is coloured by total
Non methane VOCs, with a resolution of 1 km grid boxes. Image courtesy
of DEFRA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.4 A representation of the Hadley cell, indicating air flows that create the cell.
1) Sunlight heats up the surface at the equator, which in turn heats up
the air parcel above. 2) This air parcel rises rapidly as it’s hotter and less
dense than the air around it. 3) The air parcel ceases to rise, and is moved
latitudinally by air rising beneath it. 4) The air parcel cools and sinks as
it becomes more dense. 5) The air moves back towards the equator to fill
the void by air rising, and heats up again, completing the cycle. . . . . . . 33
1.5 Locations of global GAW stations across the planet. . . . . . . . . . . . . . 34
1.6 Location of the LAQN sites, displaying the level of air quality on a scale of
1-10. Image courtesy of Kings College London . . . . . . . . . . . . . . . . . 35
1.7 Trends in benzene as measured by the DEFRA Automatic hydrocarbon
network. Data displayed is annual average data for benzene from the site
Image Courtesy of Defra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.8 Trends in butadiene as measured by the DEFRA Automatic hydrocarbon
network. Data displayed is annual average data for butadiene from the site
Image Courtesy of Defra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.9 Van Deemter plot of theoretical plate height against gas velocity for N , He
2
and H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2
7
List of Figures
1.10 Schematic of an Electron Multiplier detector. Ions strike the electron rich
plate, initiating a cascade of electrons, which can be detectedby a voltmeter. 45
1.11 The FAAM BAe-146-301 ARA in flight. The probes and inlets can be seen
mounted to the body, nose and under the wings, giving the aircraft the
capacity to make a large range of different measurements- from meteorol-
ogy and cloud microphysics to atmospheric composition of a wide range of
species. Image Courtesy of FAAM . . . . . . . . . . . . . . . . . . . . . . . 46
1.12 View from the rear of the aircraft during a flight, showing the lines of racks
housing the scientific instrumenation. Image Courtesy of Jim Hopkins . . . 47
1.13 Example of a configuration of instruments onboard the aircraft. . . . . . . . 48
2.1 The University of York aircraft GC/MS rack, with key components indi-
cated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.2 A schematic of the four-position valve used to change between different
sample types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.3 A schematic of the two position valve used to track mass spectrometer
sensitivity shown in both positions with the sampling position on the left
and the injecting position on the right . . . . . . . . . . . . . . . . . . . . . 56
2.4 Isoprene breakthrough tests. A total sample volume of 1 L with a flow
rate of 200 mL/min was chosen, as this was a compromise between com-
pounds breaking through, a large enough sample volume for less abundant
compounds, and a fast overall rate of sample collection. . . . . . . . . . . . 57
2.5 A flow diagram of the Thermal Desorption Unit showing all potential flow
paths. (Markes (2006)). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.6 Chromatograms of two high purity nitrogen samples showing two different
dryingmethods. ThesampleswerepassedthrougheitheralengthofNafion
tubing (black) or a glass cold finger (blue) . . . . . . . . . . . . . . . . . . . 60
2.7 CAD image of the Peltier Water trap, showing the heat sink in grey, and
the copper sheath in orange . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.8 Chromatogramshowingtheimprovementincarbontetrachloridepeakshape
withadditionofliquidCO2(inblack)refocussing, comparedtowithoutliq-
uid CO2 (in red) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.9 Schematic of the Nafion membrane water removal system used during the
CAST campaign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
8
List of Figures
2.10 SchematicdiagramofaStirlingCooler,withkeycomponentslabelled(Global
Cooling Inc.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.11 TimeprofileoftheCO Tpiece. TheblacklinesindicatewhentheCO was
2 2
turnedon, andoff. Temperaturefluctuationsareduetoicecrystalsforming
and blocking the holes where the CO is released. It is also important to
2
note the time taken for the T-piece to warm up again after the CO is
2
turned off. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.12 Extracted ion chromatogram of ion 117 (carbon tetrachloride) of two GC
analyses showing the further improvement in peak width, one in which the
CO heater was turned on for 30 seconds at the start of the run (black)
2
and one in which the CO heater was turned off during the entire run (red).
2
The peak widths are shown for comparison. . . . . . . . . . . . . . . . . . 66
2.13 A time series showing carbon tetrachloride and GC/MS averaged altitude
overthecourseofasingleflightduringCAST.Asaltitudeincreases, carbon
tetrachloride decreases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.14 A vertical profile of carbon tetrachloride during CAST, showing a large
distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.15 A vertical profile of carbon tetrachloride during Oil and Gas, showing a
reduced distribution in peak areas. . . . . . . . . . . . . . . . . . . . . . . . 68
2.16 The vertical profiles of the two flights plotted onto the same axis. The
reduction in the spread of the carbon tetrachloride data can be seen in the
Oil and Gas data (red) when compared to the CAST data (black). . . . . . 69
2.17 Schematic showing the internal electronics of the flow control box used
during the Oil and Gas campaign . . . . . . . . . . . . . . . . . . . . . . . 70
2.18 Schematic showing all flow paths in the flow control box used during the
Oil and Gas campaign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.19 Timeseriesofcarbontetrachlorideandbenzenepeakareasmeasuredduring
a 7 hour long flight simulation / calibration. . . . . . . . . . . . . . . . . . 73
2.20 Overlaid plot of the three days of calibrations run on the GC/MS, showing
how the sensitivity changes both over a flight time, and between different
days. A polynomial best fit line (2nd order) was fitted to each data series.
The statistics are shown in the table below. . . . . . . . . . . . . . . . . . 73
9
List of Figures
2.21 Correlation between carbon tetrachloride and benzene (top), and carbon
tetrachloride and benzene (bottom), observed during the 7 hour calibration 75
2.22 Correlationsbetweencarbontetrachlorideandacetone(top),andm/p xylenes
(bottom). The acetone plot is separated based on the trap used to precon-
centrate the sample, as non-uniform packing of the sorbent between traps
has a large effect on highly volatile species. . . . . . . . . . . . . . . . . . . 76
2.23 Time series of benzene peak area after the 7 hour calibration, following
applying a correction factor based on carbon tetrachloride peak area. The
scatter is significantly lower. . . . . . . . . . . . . . . . . . . . . . . . . . . 77
2.24 Timeline of campaigns and instrument modifications during the period
September 2011 to September 2015. . . . . . . . . . . . . . . . . . . . . . . 80
3.1 Extracted ion chromatogram of a calibration standard used during the
SAMBBA campaign. Ions 67, 91, 98 and 78 are extracted showing iso-
prene, benzene, toluene, ethyl benzene (with xylenes) and monoterpenes
(e.g., α -pinene). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.2 A comparison between isoprene as measured by the WAS system and the
in situ GC/MS system. The graph shows a highly scattered correlation, as
demonstrated by an R2 value of 0.55. . . . . . . . . . . . . . . . . . . . . . 89
3.3 A comparison between isoprene as measured by the PTR-MS and the in
situ GC/MS. The figure shows the PTR-MS data as averaged over the
GC/MS sample times, over the entire campaign. The two data sets show
good agreement with an R2 value of 0.75. The offset in the data can be
attributed to differences in sampling methods, as well as furan mixing ratios. 89
3.4 Aircraft position over the entire SAMBBA campaign averaged over the
GC/MS sample times. The points show the mid-sample time for each chro-
matogram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.5 Track plot of aircraft position over the entire SAMBBA campaign, coloured
by CO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.6 VerticalprofileofozonecollectedduringtheSAMBBAcampaign. The1Hz
data provided by the aircraft has been averaged over the GC/MS sample
times (5 mins) and binned to 500 m to produce the distributions. The box
and whisker plots represent the mean, median, interquartile range, bottom
5 %, top 95 % and outliers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
10