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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

Session 2 – Analytical Issues

Mercury Speciation Workshop

330 Nantucket Blvd. Toronto, Canada M1P 2P4

Rev 1.10 Nov 2003

issues in session two
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

  • 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
tests at tekran
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
temp dependent denuder variables
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
main difference with arctic air
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?
tests by frontier geosciences
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)
relevant fl dep tests
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
arctic tests
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
  • 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
when no rgm or tpm present
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
possible reasons gem
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?
possible tests gem
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 !
other reasons for differences
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
mercury chloride hgcl 2
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
mercury chloride hgcl 21
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
mercury iodide hgi 2
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%
monomethyl mercury chloride ch 3 hgci
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
further testing needed
Further Testing Needed
  • EPA NERL (Matt Landis, Bob Stevens) are planning on testing a wide variety of mercury compounds for capture efficiency
what we know
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
transport issues
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)
under arctic conditions
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
tests with prototype 1130 s
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
side by side tests
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
duplicate instruments
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
  • 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
  • Instrument flow rates are critical!
    • Must calibrate all 2537A and 1130 MFM’s before running any tests
effects of sodalime trap1
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
calibration rgm
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
calibration hgp
Calibration - HgP
  • Even more difficult !
  • Some issues:
    • Picogram amounts required
    • Controlling size distribution
    • Sample introduction
two techniques
Two techniques
  • Original super-saturated method
  • EPA method
rpf standard technique
RPF Standard Technique
  • There is none !