Session 2 analytical issues
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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

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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

1Do 1130 & 1135 work in the Arctic ?

2What Species do denuders measure ?

3What does a Model 2537A measure ?

4Precision & Accuracy of method

5Effects of sodalime trap

6Calibration for RGM & HgP

7Denuder coating techniques

8RPF refill techniques


Do the model 1130 1135 work in the arctic

Do the Model 1130 & 1135 Workin the Arctic?


Caveats

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


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


Results

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


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


What species do thermally regenerated kcl denuders measure

What Species Do Thermally Regenerated KCl Denuders Measure?


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


Is there a simple answer

Is there a simple answer ?

What does a Model 2537A actually measure ?


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


Caveats for duplicate instrument runs

Caveats for duplicate instrument runs

Precision & Accuracy


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


Early results toronto

Early Results - Toronto


Early results toronto1

Early Results - Toronto


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


Caveats1

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


Caveats2

Caveats

  • Instrument flow rates are critical!

    • Must calibrate all 2537A and 1130 MFM’s before running any tests


Effects of sodalime trap

Effects of Sodalime Trap


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 for rgm hgp

Calibration for RGM & HgP ?


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


Denuder coating techniques

Denuder Coating Techniques ?


Two techniques

Two techniques

  • Original super-saturated method

  • EPA method


Rpf refill techniques

RPF Refill Techniques ?


Rpf standard technique

RPF Standard Technique

  • There is none !


End of session 2

End of Session 2


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