eckley, c.sa., gustin, m ., lin, c. j. li, x. miller, m.b...40 60 80 100 120 140 0:00 6:00 12:00...
TRANSCRIPT
![Page 1: Eckley, C.Sa., Gustin, M ., Lin, C. J. Li, X. Miller, M.B...40 60 80 100 120 140 0:00 6:00 12:00 18:00 0:00 Hg Flux (ng/m. 2 /h) Time of Day. Hg Flux. 24 hour Flux Data • 24 hour](https://reader031.vdocuments.net/reader031/viewer/2022011909/5f73b137064eb029955277f8/html5/thumbnails/1.jpg)
Mercury Flux Measurements Methods in Nevada, USA
Eckley, C.Sa., Gustin, Ma., Lin, C.‐J.b, Li, X.c
, Miller, M.B.a
aDepartment of Natural Resources & Environmental Science, University of Nevada, Reno, NV USAbDepartment of Civil Engineering, Lamar University, USAcDepartment of Mechanical Engineering, Lamar University, USA
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Presentation Outline
•
Introduction to surface‐air fluxes
•
Measurements –
Equipment
–
Site conditions
–
Data interpretation
•
Flux chamber design experiments
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Source:
UNEP
Global Hg Partnership Interim Report, 2008
Introduction: surface‐air fluxes
HgPoint sources
Terrestrial non‐point source emissions are an important component of the global Hg cycle
Hg
Non‐point sources
1,805 Mg/yr
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2 main methods used to measure surface-air Hg flux:
Introduction: surface‐air fluxes
2) Micrometeorological Gradient Method
1) Dynamic Flux Chambers (DFC)Flux = (Cinside
‐
Coutside
) *(Q/A)
Hg
Surface
Hg
HgHg
Hg
To Tekran
Hg Air Conc
at 2.2 m
Hg Air Conc
at 0.2 m
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Set‐up: Equipment
Figure from Lindberg et al., 2002
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Set‐up: Equipment•
Tekran 2537A/B Mercury Vapour Analyzer•
Tekran Model 1110 Synchronized Two Port Sampling System (TADS)•
Tekran 2505 Mercury Vapour Calibration Unit•
Generator (Honda EU2000iA)•
Line conditioner (Tripp Lite
Line Conditioner)•
Surge protector•
Argon gas•
Flush pump(s)•
Flow meter•
Teflon tubing (insulation)•
Teflon tape•
Silicon tubing connectors•
Soda lime traps•
Air filters (0.22 µm;PTFE)
•
Fan/heaters•
Laptop computer•
Dynamic Flux Chamber
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Set‐up: Equipment
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Set‐up: Equipment
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•
Ancillary data:–
Meteorological Measurements
•
Solar radiation
•
Temperature
•
Relative humidity
•
Wind speed/direction
•
Precipitation (tipping bucket)
–
Soil moisture content
–
Soil Hg conc. under chamber
Set‐up: Equipment
0100200300400500600700800900
0:00 6:00 12:00 18:00 0:00Time of Day
Hg
Flux
(ng/
m2/
h)
0100200300400500600700800900
Sola
r Rad
iatio
n (W
/m2)Hg Flux
Sol Rad
020406080
100120140160180200
01/00/00 01/20/00 02/09/00 02/29/00 03/20/00 04/09/00
Hg
Flux
(ng/
m2 /h
)
Hg Flux
Time (hours of sampling)
dry
wet
Hg Flux Hg & Solar RadiationHg Flux vs
Soil Hg
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•
Location
—Surface variability (important for scaling)
–
Stable ambient air concentrations
Set‐up: Sampling Considerations
Variable Hg Air Concentrations
-20
0
20
40
60
80
100
120
140
0:00 6:00 12:00 18:00 0:00
Hg
Flux
(
ng/m
2 /h)
Time of Day
Hg Flux
24 hour Flux Data
• 24 hour measurements
Gustin et al (2008) JAWMA
-10
-5
0
5
10
15
20
25
0 50 100 150 200 250 300 350 400
Time (days from start of expt)
Hg
flux
(ng/
m2
h)
June
'05
Aug
'05
Nov
'05
Feb
'06
w
May
'06
Aug
'06
Seasonal Hg Flux
• Seasonal measurements
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•
Chamber blanks
Set‐up: Equipment
Blank chamber: similar conditions to sampling
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Sample Results—Good Data
Surface
To Tekran
Inlet Air1
Flux = (Cinside
‐Coutside
) *(Q/A)
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Sample Results—Good Data
Surface
To Tekran
Outlet Air
10
Flux = (Cinside
‐Coutside
) *(Q/A)
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Sample Results—Good Data
Surface
To Tekran
10Flux Calculation
AVE (25, 25)‐
AVE(2,3) = 22 (ng/m3)Delta C Flux = (Cinside
‐Coutside
) *(Q/A)
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Sample Results—Good Data
Surface
To Tekran
10Flux Calculation
22 (ng/m3)×
0.17 (m3/h) ÷
0.036 (m2)= 106 (ng/m2/h)Flux Flux = (Cinside
‐Coutside
) *(Q/A)
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Sample Results—Bad Data
Surface
To Tekran
Criteria for accepting/rejecting a flux:1) The delta C must be larger than the difference between the 2 inlets
16 (ng/m3) > 29 (ng/m3) Cannot Accurately Calculate Flux
2) The difference between the 2 outlets must be smaller than the outlet average258‐74 =
184 (ng/m3)
<
AVE(258,74) = 166 (ng/m3) Cannot Accurately Calculate Flux
Flux = (Cinside
‐Coutside
) *(Q/A)
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Surface
To Tekran
Sample Results—Good & Bad DataFlux = (Cinside
‐Coutside
) *(Q/A)
Ideal Flux Sampling Conditions:Stable Ambient Air Concentration: 1.6 to 4.7 ng/m3
All flux data was acceptable
Poor Flux Sampling Conditions:Unstable Ambient Air Concentration: 15 to 350 ng/m3
33 % of flux data was acceptable
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Dynamic Flux Chamber Design:
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Area (m2)
Volume (L)
Flow (L/min)
TOT(min)
Material Researcher
0.16 32 2.0 16 Stainless steel Schroeder et al. 1989
0.13 25 1.8 13.9 Teflon He et al., 1998
0.12 24 3.2 7.5 Acrylic Magarelli & Fostier, 2005
0.073 11.2 1.5 7.5 Polycarbonate Kuiken et al., 2008
0.13 10 1.5 6.7 Stainless steel/Teflon Poissant & Casimir, 1998
0.12 24 5 4.8 Teflon Carpi and Lindberg, 1998
0.12 24 6 4 Plexiglass Ferrara & Mazzolai, 1998
0.12 24 6 4 Teflon Zhang et al., 2001
0.03 2.2 1.5 1.5 Teflon Zhang et al., 2008
0.063 3 2.3 1.3 Polycarbonate Eckley & Branfireun, 2008
0.036 1.5 1.5 1 Polycarbonate Ericksen and Gustin, 2006
0.06 4.7 15 0.31 Quartz Wang et al., 2005
NA 2 6.7 0.30 Polycarbonate Gustin & Stamenkovic, 2005
0.031 1 6.5 0.15 Polycarbonate Nacht & Gustin , 2004
0.031 1 10 0.10 Polycarbonate Engle et al., 2001
Large diversity of
DFC
designs and flow rates
DFC
Design:
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Research Objectives:
Compare DFCs with different:1) materials2) volumes3) port placements4) flow rates
Question: How does flux chamber design influence the quantification of Hg emissions?
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Several studies address the influence of these variables:
Wallschlager
et al., 1999Flux increases with flow; high flows recommended
Gillis & Miller, 2000No flow recommendations—they felt their flows (1‐10
lpm) were below optimal
Zhang et al., 2002 & Lindberg et al., 2002 Low flows may underestimate fluxes—recommend high flow: 15 to 40
lpm
Engle et al, 2006Optimal flow rate may vary with magnitude of surface emissions
Flushing Flow Rate (& Chamber Volume)
Chamber Material
Carpi
et al., 2007
Polycarbonate chambers may underestimate flux relative to Teflon
Introduction:
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DFC: Chamber Material
Material: PolycarbonateThickness: 3.7 mmVolume: 1.5 LArea:0.038 m2
Flow (TOT): 1.13
lpm
(1.32)
Material: Teflon Thickness: 0.19 mmVolume: 2 LArea: 0.036 m2
Flow (TOT): 1.5
lpm
(1.36)
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0
100
200
300
400
500
600
700
800
0:00 6:00 12:00 18:00 0:00
Time of Day
Hg F
lux
(ng/
m2 /h
)
0
200
400
600
800
1000
1200
Sola
r Ra
diat
ion
(W/m
2 )TeflonPolycarbSol Rad
DFC: Chamber Material
Surface Material: Mine Tailings (30.1 µg/g)Polycarbonate
vs
Teflon
Teflon Flux:
298 ng/m2/h
Polyc. Flux:
204 ng/m2/h
(p < 0.001)
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Teflon Flux:
325 ng/m2/h
Polyc. Flux:
207 ng/m2/h
(p < 0.001)
0
100
200
300
400
500
600
700
800
0:00 6:00 12:00 18:00 0:00
Time of Day
Hg F
lux
(ng/
m2 /h
)
0
200
400
600
800
1000
1200
Sola
r Ra
diat
ion
(W/m
2 )TeflonPolycarbSol Rad
DFC: Chamber Material
Surface Material: Mine Tailings (30.1 µg/g)Polycarbonate
vs
TeflonSunlight Hours Flux
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-5
0
5
10
15
20
12:00 13:12 14:24 15:36 16:48 18:00
Time of Day
Hg
Flux
(ng/
m2 /h
)
Teflon
Polycarb
DFC: Chamber Material
Polycarbonate
vs
Teflon
Chamber Blanks (post‐sampling w/o acid cleaning)
Teflon Flux:
2.4 ng/m2/h
Polyc. Flux:
7.0 ng/m2/h
(p = 0.001)
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•
Teflon DFC blanks were lower than polycarbonate (with & without acid cleaning)
•
Teflon DFC Hg fluxes were higher than polycarbonate for 2 of 3 substrates--
Daily average relative difference: 46 ±12 %Hourly maximum relative difference: 107%
DFC: Chamber Material
Polycarbonate
vs
TeflonConclusion:
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DFC: Chamber Volume
Small
DFCMaterial: PolycarbonateThickness: 3.7 mmVolume: 4.05 LArea:0.063 m2
Flow: 1.5 – 4.1 lpm
Large
DFCMaterial: Polycarbonate Thickness: 3.7 mmVolume: 10.00 LArea: 0.071 m2
Flow: 1.5 ‐
9.9
lpm
Surface Material: 1.3 µg/g
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DFC: Chamber Volume
0
50
100
150
200
250
300
350
400
0:00 6:00 12:00 18:00 0:00Time of Day
Flux
(ng/
m2 /h
)
0
200
400
600
800
1000
1200
Sol R
ad (W
/m2 )
Small DFC
Large DFC
Sol Rad
Small
DFC
Flux: 134 ng/m2/h Large
DFC
Flux: 78 ng/m2/h
Small
DFC
Flow: 1.5 L/min
TOT: 2.2Large
DFC
Flow: 1.5 L/min
TOT: 6.7Air‐stream velocity:
5.0 m/h2.0 m/h
Same Flow Rate
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DFC: Chamber Volume
0
200
400
600
800
1000
1200
1400
1600
0:00 6:00 12:00 18:00 0:00Time of Day
Hg F
lux
(ng/
m2 /h
)
0
200
400
600
800
1000
1200
Sol
ar R
adia
tion
(W/m
2 )
Large DFCSmall DFCSol Rad
Small
DFC
Flow: 4.1 L/min
TOT: 1.1 Large
DFC
Flow: 9.9 L/min
TOT: 1.0
Small
DFC
Flux: 351 ng/m2/h Large
DFC
Flux: 579 ng/m2/h
Air‐stream velocity:
13.4 m/h13.2 m/h
Small
DFC
Δ
C: 91 ng/m3
Large
DFC
Δ
C: 68 ng/m3
Same TOT
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DFC: Chamber Volume
Conclusion:
•
At the same flow, the smaller chamber has a higher air-stream velocity over the surface which may enhance emissions
•
At the same TOT (& velocity), the larger chamber has a greater Hg emission potential due to a lower chamber air concentration and/or a higher flushing flow rate promoting release of Hg from the surface
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DFC: Port Placement
Side port
Top port
To Analyzer
Air flowAir flow
3-day comparison:Side port: 13.5 ± 9.3 ng m-2 h-1
Top port: 13.7 ± 4.1 ng m-2 h-1
( t = 2.0, p = 0.89)
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DFC: Chamber Flushing Flow
0
5
10
15
20
0 5 10 15 20 25 30 35Flow (lpm)
Del
ta C
(ng/
m3 )
Surface Material:Alluvium (0.5 µg/g)
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35Flow (lpm)
Hg
Flux
(ng/
m2 /h)
Typical wind speed at 0.1m:0 to 70 m/h(depending on surface roughness)
0
5
10
15
20
0 5 10 15 20 25 30 35Flow (lpm)
Del
ta C
(ng/
m3 )
0
20
40
60
80
100
120
Airs
tream
Vel
ocity
(m/h
)
Target zone for
measuring flux
Flux = (Cinside
‐Coutside
) *(Q/A)
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DFC: Chamber Flushing FlowIdeal flow rate would create conditions inside the chamber similar to those outside the chamber
Competing criteria: similar air flow vs
similar air Hg concentration gradient
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DFC: Chamber Flushing FlowSurface Material:Mine Tailings (30.1 µg/g)
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
Flow (lpm)
Hg
Del
ta C
(ng/
m3 )
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30Flow (lpm)
Hg
flux
(ng/
m2 /h)
Target zone for
measuring flux
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DFC: Chamber Flushing FlowConclusion:
Ideal flow rate and TOT vary with the strength of the emission
Flow rates can have a larger influence on calculated Hg emissions
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Flux changes on diel cycle—therefore sometimes TOT will be less than ideal
DFC: Chamber Flushing Flow
0
100
200
300
400
500
600
700
800
900
1000
0:00 6:00 12:00 18:00 0:00
Time of Day
Hg
Flux
(ng/
m2 /h)
0
200
400
600
800
1000
Sola
r Rad
iatio
n (W
/m2 )
Flux
Solar Radiation
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Overall Conclusions
Question: How does flux chamber design influence the quantification of Hg emissions?
1) materials
2) volumes
3) port placements
4) flow rates
< 1‐fold difference
< 1‐fold difference
No difference
> 7‐fold difference
Questions: [email protected]