Tracer release experiments

1
Tracer release experiments

• Damien Martin, Catheryn Price, Tony Makepeace,
  Graham Nickless, Peter Simmonds, Brian Greally,
  Alan Knights, Simon ODoherty and Dudley
  Shallcross,
• Rex Britter and Marina Neophytou.
• University of Bristol and University of Cambridge

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Outline

• Tracer methodology brief review
• First results from DAPPLE I
• On-going developments
• Thoughts on DAPPLE II
• Acknowledgements

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Tracer properties required

• Non-toxic
• Inert (long lifetime)
• Non-depositing
• Low background concentration
• Sensitive detection method
• Answer Perfluorocarbon tracers (SF6)

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Perfluorocarbons

• Typical background concentrations ppq
• Can be separated from air sample using Gas
  Chromatography and detected using negative ion
  chemical ionisation (NICI) mass spectrometry
• Perfluoromethylcyclohexane (PMCH)
• Perfluoromethylcyclopentane (PMCP)

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The Apparatus

• GC-MS system
• Tracer release equipment (cylinders)
• Sampling system

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Schematic of GC-MS system
Air sample
NICI-MS
PC
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Separation of PDMCH isomers

• Carbograph PLOT Column
• NOTE
• PMCP
• (methyl cyclopentane)
• PMCH
• (methyl cyclohexane)
• o c PDCH
• (ortho cis dimethyl cyclo hexane)

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Automated Bag Samplers

• Battery Operated Bag Sampler
• Internal pump to air intake
• Controller is chip based, this automates sample
  sequence Internal clock to control times
• Solenoid controller flow block determines which
  bag is filled
• Tedlar bags attach to Teflon tubing - 3L air
  target for background concentration
• Sampling time determined by volume of Tedlar bag
  (to 5L) and release rate of tracer.

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Protocol for release

• Tracers sealed in cylinders and transported to
  site.
• Release apparatus set up 1 hour before expt. to
  allow system to stabilise.
• All tubing is flushed prior to arrival at site.
• Weight loss of all tracers and pressure drop on
  all cylinders monitored throughout the expt.
• Entire release system is sealed and all samplers
  collected and closed and transported off site,
  then release system removed to avoid accidental
  post-release.

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Release regime

• Release both PMCH and SF6 from same site in York
  Street (see later)
• Release PMCH for 15 mins.
• Release SF6 for 15 mins. but offset by 1.5 mins,
  i.e. SF6 release starts after PMCH.

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Problems to overcome

• Iraq war, security, releasing chemicals in London
  !
• Safety of personnel and equipment during
  experiment.
• Access to suitable release sites.
• A major achievement under these circumstances.

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Results from DAPPLE I 15/5/03
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Results from DAPPLE I 15/5/03
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On-going developments

• Rest of analysis to be completed by mid August.
• Developing capability to release 3 PFC tracers
  (PMCH, PMCP, o c DMPCH) separately.
• Developing a real-time analyser for PFCs (1
  minute sampling) and same for SF6
• Hope to be able to release 3 tracers in 3
  locations simultaneously and to have 1 real-time
  analyser available for DAPPLE II.

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Thoughts on DAPPLE II

• Propose to plan for three different release
  experiments, with location of samplers and
  release sites to be discussed with Rex in
  September.
• We should then be able to take advantage of any
  (most) wind directions.
• Use of several tracers should be extremely
  illuminating, where several problems can be
  tackled simultaneously. Real-time data will we
  hope also provide useful information.

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Conclusions

• First release was a success, amount released was
  about right, i.e. did not overload the analysers
  and was not too small.
• Already some interesting observations, no tracer
  at the end of York Street, similar levels at roof
  and ground level of W.C.C.

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Acknowledgements

• EPSRC DAPPLE
• MSG MOD
• NERC - studentship

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Adsorbent-filled Macrotrap Samplers

• Automated Macrotrap sampler
• Internal processor controlled
• Programmed to sample 3 litres of air onto
  macrotraps followed by isolation of the trap
  until lab analysis possible
• 15 traps per box - up to 5 hours sampling time
• Macrotraps undergo thermal desorption into ADS
  system in central laboratory

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Release monitoring (pressure)