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Session 2 – Analytical Issues

Session 2 – Analytical Issues. Mercury Speciation Workshop. 330 Nantucket Blvd. Toronto, Canada M1P 2P4. Rev 1.10 Nov 2003. Issues in Session Two. 1 Do 1130 & 1135 work in the Arctic ? 2 What Species do denuders measure ? 3 What does a Model 2537A measure ?

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Session 2 – Analytical Issues

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  1. Session 2 – Analytical Issues Mercury Speciation Workshop 330 Nantucket Blvd. Toronto, Canada M1P 2P4 Rev 1.10 Nov 2003

  2. Issues in Session Two 1 Do 1130 & 1135 work in the Arctic ? 2 What Species do denuders measure ? 3 What does a Model 2537A measure ? 4 Precision & Accuracy of method 5 Effects of sodalime trap 6 Calibration for RGM & HgP 7 Denuder coating techniques 8 RPF refill techniques

  3. Do the Model 1130 & 1135 Workin the Arctic?

  4. Caveats • The following is not based upon any actual arctic measurements • There is currently no reliable RGM calibration source that would work under those conditions • Tekran doesn’t go up there often • We don’t have an environmental test chamber

  5. Tests at Tekran • Tests were continuously run during the year it took to deliver first Model 1130-P prototypes (May 1998) • Initial tests used packed cartridges • Subsequent tests used thermal denuder • Tests were run using outdoor air in Toronto • Summer: +30° C, (typical moist summer air) • Winter: -20° C, (typical dry winter conditions) • Method worked well under full seasonal range

  6. Temp Dependent Denuder Variables • Diffusion coefficient of HgCl2 • Low temps could reduce capture efficiency • Actual gas volume of sample (p,v) • Affects residence time in denuder • Low temps increase residence time • Gas is pre-heated by impactor and denuder inlet • Approx inlet volume is 80 ml • Heating residence time is ~0.45 sec. (at 10 l/m) • Actual gas temp at denuder inlet will not be close to -40° C

  7. Main Difference with Arctic Air • The major difference between arctic air and temperate air is the moisture content of the air • After heating, the air will be very dry • Does the 1130 capture RGM under low humidity conditions?

  8. Tests by Frontier Geosciences • Two prototype 1130’s purchased by Florida DEP were extensively tested by Eric Prestbo in 1998 • Contract funded by Tom Atkeson of FL DEP • Formal report never issued • Results were presented at several conferences and incorporated into Landis et. al. (ES&T, 2002)

  9. Relevant FL DEP Tests • Tests were done using: • Nitrogen from a dewar • Ambient air • Sample gas created from a dewar was extremely dry • No significant differences in capture efficiency were detected between very dry gas sample and ambient samples

  10. Arctic Tests • Alert: Bill Schroeder ran two different systems in parallel • Arctic Pyrolyzer • No inlet filter • Large pyrolyzer, 900 °C with lengthy residence time • Feeds into a Model 2537A • Expected to yield total atmospheric mercury (TAM) (both gaseous and particulate forms) • Model 1130/1135/2537A

  11. Results • During non-depletions • Fairly good agreement between the methods • Hg0 (GEM) slightly lower in 1130/35 system • During MDEs • Some differences, typically 20-30% with pyrolyzer being higher (personal communication S. Steffen, B. Schroeder) • Shows that there is no gross failure of the 1130/1135 method in the Arctic, even during MDEs

  12. When No RGM or TPM Present Pyro TAM ~0.2 ng/m3 higher than GEM measured through 1130/35 • There may be slight contamination in pyrolyzer system • Material in pyro chamber • Downstream heated line • There may be scavenging in 1130/35 • RPF, downstream filter or internal lines • Heated line or fittings around PM

  13. Possible Reasons - GEM • Should review Arctic QA/QC data to determine: • Do TAM values decrease after cleaning of the pyrolyzer and downstream heated line & fittings? • Have zero checks and manual injection tests of entire pyrolyzer system revealed any problems?

  14. Possible Tests - GEM • Could perform external zero and Hg0 addition system test on 1130/35 • Requires 10 l/m zero air source • Manual injection source & syringe (large volume syringe: 100-250 µl) • Must first perform accurate flow rate tests on both 2537A and 1130 pump! • Required to determine what fraction of injected Hg will disappear through PM • Tricky test !

  15. Other Reasons for Differences • Two devices are measuring slightly different things: • Pyro measures total particulate loading • 1130/35 measures fine fraction particulates (< 2.5 µm) • Difference could be legitimate • Some mercury may be in coarse particulate fraction • Could also be losses of RGM on inlet surfaces • Dirty impactor surfaces • Insufficient heating

  16. What Species Do Thermally Regenerated KCl Denuders Measure?

  17. Mercury Chloride - HgCl2 • Compound most often used as a surrogate for “RGM” • Reasonable choice since it’s believed to be created by many industrial sources • Believed to be the bulk of RGM loadings

  18. Mercury Chloride - HgCl2 • Extensively tested by Tekran • Major pain to work with • Extremely “sticky” • Regenerable KCl media had >98% capture efficiency • Initial work with KCl coated quartz chips • Subsequently validated using denuders

  19. Mercury Iodide – HgI2 • Originally tested as a substitute for HgCl2 • Hoped that it would be easier to work with • Turned out to be exactly as much of a pain • Behaved the same as HgCl2 with a capture efficiency: >98%

  20. Monomethyl mercury chloride – CH3HgCI • Tested by Jonas Sommar (Sweden) • Tests pre-dated thermal method • Used tubular denuder with wet extraction & digestion • Reported a capture efficiency: >94% • (In comparison to 98% for HgCl2) • Don’t have a publication reference

  21. Further Testing Needed • EPA NERL (Matt Landis, Bob Stevens) are planning on testing a wide variety of mercury compounds for capture efficiency

  22. Is there a simple answer ? What does a Model 2537A actually measure ?

  23. What We Know • The Model 2537A will respond to HgCl2 that is presented to the cartridges • Ontario Hydro, 1995 (?) • Had to bypass all front end components to get HgCl2 into the cartridges • We can’t claim that the 2537A is an elemental Hg analyzer

  24. Transport Issues • HgCl2 does not transport well through sample lines or filters • Will stick onto the materials • May come off later depending on factors such as: • Temperature • Humidity • Composition of sample • ERG & EPA (1997-98)

  25. Under Arctic Conditions • Model 2537A functions basically as an elemental Hg analyzer • Evidence: MDE’s were originally discovered by Env. Canada • 2537A recorded very low values • We now know that lots of RGM was present during many of those events

  26. Caveats for duplicate instrument runs Precision & Accuracy

  27. Tests with Prototype 1130’s • Our outdoor air was brought in through a 4” plastic pipe using a 700 l/m blower • Both units ran from same pipe • We do not claim that sample contained true outdoor RGM levels • Got good agreement between units

  28. Side by side Tests • Indoor air was simply taken in by the two 1130’s mounted side by side • Not as good agreement for RGM. Why? • Denuders more precise at lower concentrations • Outdoor air works better than indoor air • Sampling wasn’t from a common manifold

  29. Early Results - Toronto

  30. Early Results - Toronto

  31. Duplicate Instruments • Running two instruments side by side is not trivial • Must be sampling exactly the same air • Even minor differences in location will have a large impact • Have seen this with 2537A for years • Much more of an effect with RGM/HgP

  32. Caveats • Sampling manifold issues • First instrument in chain will contaminate sample manifold when blowing back zero air during desorption • Precise syncing will help, but not eliminate this problem • Transport of RGM & HgP along manifold • Effect of intrusion by sampling inlets • Scavenging/contamination • Isokinetic sampling if monitoring particulates

  33. Caveats • Instrument flow rates are critical! • Must calibrate all 2537A and 1130 MFM’s before running any tests

  34. Effects of Sodalime Trap

  35. Effects of Sodalime Trap • Works well in most cases • Bad sodalime can either scavange or augment mercury from sample • Good sodalime can go bad simply by being stored after opening • Must be kept above dew point of sample air

  36. Calibration for RGM & HgP ?

  37. Calibration - RGM • Very difficult to get long term stability in lab • Even harder in the field • Likely to be used as a check, rather than as an actual calibration source

  38. Calibration - HgP • Even more difficult ! • Some issues: • Picogram amounts required • Controlling size distribution • Sample introduction

  39. Denuder Coating Techniques ?

  40. Two techniques • Original super-saturated method • EPA method

  41. RPF Refill Techniques ?

  42. RPF Standard Technique • There is none !

  43. End of Session 2

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