Session 2

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 Work in 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 doesnt go up there often
• We dont 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 1130s 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. (EST, 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 (lt
  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 its 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 gt98 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 gt98

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 gt94
• (In comparison to 98 for HgCl2)
• Dont 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
What does a Model 2537A actually measure ?

• Is there a simple answer ?

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 cant 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 MDEs 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
Precision Accuracy

• Caveats for duplicate instrument runs

27
Tests with Prototype 1130s

• 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 1130s
  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 wasnt 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 MFMs 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