1. Tracer release experiments
Damien Martin, Catheryn Price, Tony Makepeace, Graham Nickless, Peter Simmonds, Brian Greally, Alan Knights, Simon O’Doherty and Dudley Shallcross,
Rex Britter and Marina Neophytou.
University of Bristol and University of Cambridge
Tracer Dispersion Studies

2. Tracer Dispersion Studies
Outline
Tracer methodology – brief review
First results from DAPPLE I
On-going developments
Thoughts on DAPPLE II
Acknowledgements
Tracer Dispersion Studies

3. Tracer properties required
Non-toxic
Inert (long lifetime)
Non-depositing
Low background concentration
Sensitive detection method
Answer: Perfluorocarbon tracers (SF6)
Tracer Dispersion Studies

4. Tracer Dispersion Studies
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)
Tracer Dispersion Studies

5. Tracer Dispersion Studies
The Apparatus
GC-MS system
Tracer release equipment (cylinders)
Sampling system
Tracer Dispersion Studies

6. Schematic of GC-MS system
Air sample
ADS GC
NICI-MS PC
Tracer Dispersion Studies

7. Separation of PDMCH isomers
Carbograph PLOT Column
NOTE:
PMCP
(methyl cyclopentane)
PMCH
(methyl cyclohexane)
o c PDCH
(ortho cis dimethyl cyclo hexane)
Tracer Dispersion Studies

8. 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.
Tracer Dispersion Studies

9. Tracer Dispersion Studies
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.
Tracer Dispersion Studies

10. Tracer Dispersion Studies
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.
Tracer Dispersion Studies

11. Tracer Dispersion Studies
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.
Tracer Dispersion Studies

12. Tracer Dispersion Studies
York Street
Library
Bickenhall Street
Westminster
Council House
Gloucester Place
Thornton Place
Bickenhall Mansions
Baker Street
Marylebone Road x
X = tracer release site 1 3 2 6 7 8 5 4 9 10
Tracer Dispersion Studies

13. Results from DAPPLE I 15/5/03
Tracer Dispersion Studies

14. Results from DAPPLE I 15/5/03
Tracer Dispersion Studies

15. 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.
Tracer Dispersion Studies

16. Tracer Dispersion Studies
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.
Tracer Dispersion Studies

17. Tracer Dispersion Studies
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.
Tracer Dispersion Studies

18. Tracer Dispersion Studies
Acknowledgements
EPSRC – DAPPLE
MSG – MOD
NERC - studentship
Tracer Dispersion Studies

19. 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
Tracer Dispersion Studies

20. Release monitoring (pressure)
Tracer Dispersion Studies