Measurement of Ammonia Concentrations and Fluxes: Recent Examples Using Denuder and Chemiluminescence Technologies
John Walker
U.S. Environmental Protection Agency National Risk Management Research Laboratory Air Pollution Prevention and Control Division Research Triangle Park, NC 27711
NADP Annual Technical Committee Meeting and Ammonia Workshop,
20-22 October 2003, Washington, D.C.
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Ammonia Research within U.S.EPA/NRMRL/APPCD
• Development of Emission Factors for Animal Production
Bruce Harris, Richard Shores, and Susan Thorneloe Swine, Poultry, Cattle OP-FTIR/TDL with computed tomography
• Natural emissions, atmospheric chemistry and deposition
John Walker Spatio-temporal variability in NH3/NHx, air/surface exchange over crops, soil emissions
NH3
NH4+
Outline
• Annular Denuder – Ambient monitoring in eastern North Carolina • Chemiluminescence NH3 Analyzer – Air/surface exchange of NH3 • Passive Denuder – Spatial gradients in the vicinity of a swine production facility
NH3
NH4+
Ambient Ammonia and Ammonium Aerosol across an Area of Variable Ammonia Emission Density
Co-authors
Wayne Robarge
North Carolina State University, Department of Soil Science, Raleigh, NC 27695
Dave R. Whitall
Center for Coastal Monitoring and Assessment, NOAA, Silver Spring, MD 20910
Hans W. Paerl
University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, NC 28557
NH3
NH4+
Background: Ammonia in North Carolina
• Eastern North Carolina contains some of the highest county-scale NH3 emission rates in the U.S. (Sampson and Duplin Counties; Strader et al., 2001). • Livestock and fertilizer account for 90% (116,000 tons N) of statewide NH3 emissions.
NH3
NH4+
Background
• Objective: Measurement of ambient NH3, NH4+, HCl, Cl-, HNO3, NO3-, SO2, SO42-, and HONO concentrations at sites in eastern NC. • Period:
Sites Clinton Kinston Morehead City
2000
County-Scale Emission Density (kg NH3 km-2) 4800 2280 320
NH3
NH4+
2000 County-Scale NH3 Emissions (CMU V2.0)
* *
< 500 500 to 750 750 to 1000 1000 to 1500 1500 to 2000 2000 to 3000 3000 to 5000 > 5000
*
Morehead City Kinston Clinton
Emission Density (kg NH3 km-2)
N
Methods
Teflon Filter Pack Contains Teflon and nylon Filters capture fine particulates containing ammonium and other species.
AIR FLOW
Denuder Tube Concentric cylinders of etched glass are coated with citric acid. NH3 molecules are retained in this section. Denuder Tube Concentric cylinders of etched glass are coated with sodium carbonate (base). Acid molecules (HCl, HONO, HNO3, SO2) are retained in this section.
Air Intake
Cyclone Stops particulates >2.5 m in size from entering annular denuder system.
Schematic of assembled annular denuder system
Results: Annual Concentrations
6 5 4
\\\ Clinton xx Kinston // Morehead City
ug m-3
3 2 1 0
NH3
SO2
HNO 3 HONO HCl
NH 4+
NO 3-
SO 4=
Cl
-
------------------------- Gas --------------------------- --------------
Aerosol --------------
Results: Ammonia/Ammonium Fractionation
0.9 0.8 0.7
Percent
NH3/(NH3 + NH4+)
0.6 0.5 0.4 0.3 0.2 0.1 0.0 W Sp Su F W Sp Su F W Sp Su F
10 Kinston 9 Spring/Summer 8 7 6 5 4 3 2 1 0 0 90 180 270 Wind Direction
360
9 8 7 6 5 4 3 2 1 0 0
Kinston Fall/Winter
Percent
90 180 270 Wind Direction
360
Clinton
Kinston
Morehead City
Results: Inorganic PM2.5
10 9 8 7
SO 4= NO 3NH 4+ Cl -
ug m -3
6 5 4 3 2 1 0 W Sp Su F W Sp Su F W Sp Su F
Clinton
Kinston
Morehead City
Results: Aerosol Formation
Excess NH 3 NH 3 NH 4 2 SO4 NO3 HNO3 Cl HCl
500 450
Excess NH 3 (nmol m -3)
400 350 300 250 200 150 100 50 0 -50 W Sp Su F W Sp Su F W Sp Su F
Clinton
Kinston
Morehead City
Conclusions
• At the three sites investigated in this study, ambient levels of NH3 and inorganic PM2.5 exhibit a positive correlation with local NH3 emission density. • NH4+ aerosol formation appears to be acid-gaslimited at the Clinton site during all seasons and during the spring and summer at the Kinston site. • NH4+ aerosol formation may, therefore, be more sensitive to changes in SO2 and NOx emissions reductions in NH3 enriched areas.
NH3 NH4+
Air Surface Exchange of NH3 over Agricultural Crops
• Objective: Measurement of NH3 exchange over soybean, corn and winter wheat using the modified Bowen ratio approach. Period: 2002 – 2003 Site: Duplin County, NC Coastal Plain
• •
NH3
NH4+
Theory
Eddy Covariance
Fy wy
dy Fy K y dz
y = momentum (u), heat (), mass (c)
K-theory
In this case, y = H2Ov, CO2, and
Modified Bowen-ratio
FNH 3
dNH 3 K y dz
NH3 NH4+
Methods: Equipment
NH3 gradient – Chemiluminescence
CO2/H2O gradient – LI6262 Temperature gradient – Thermocouple Eddy Covariance CO2/H2O/Heat fluxes LI7500/Gill Windmaster Pro
Inlet Heights – 1 and 6m 15 min. switching time Heated sample lines Hourly gradients Hourly RH PAR/Net radiation Rainfall Soil volumetric water Soil heat flux
Weekly - LAI Leaf total N Soil extractable NH4+/NO3-
NH3 flux tower - Duplin Co., NC
Methods: Tower NH3 Configuration
Upper Inlet
Heated Sample Line 8.5 Lpm
Solenoid Valve
Mobile Lab
6.2 m
NH3 Analyzer
Lower Inlet
Nt Converter
11.4 m
Methods: Chemiluminescence
NOx
Nt Converter PMT
Inlet
Nt NO
NOx Converter
Rx Cell
Nt Converter Module
NH3/NOx/NO Analyzer
Nt converter at 825 oC converts NHx + NOx to NO NOx converter at 325 oC converts NOx to NO
Routine calibration with NO standard Converter efficiency test with NH3 standard Converter efficiency typically 65 – 85%
NH3 NH4+
Methods: Gradient Detection Limit
Analyzer Precision
6
%CV (15 Min. Ave.)
5 4 3 2 1 0 0 10 20 NH3 (ppb) Converter 1 Converter 2 Power (Converter 1) Power (Converter 2) 30 40 y = 17.331x
2 -0.9058
y = 8.084x-0.5231 R = 0.9023
2
R = 0.9505
NH 3H 1 NH 3H 2 D.L.(%Diff .) 13.1 2
0.76
Methods: Response Time
Zero Air Off at Tower Inlet
25 20
NH3 (ppb)
15 10 5 0 -5 0 50 100 150 200 250 300
Seconds
Zero Air On at Tower Inlet
12 10
NH3 (ppb)
8 6 4 2 0 -2 0 50 100 150 200 250 300
Seconds
Methods: Instrument Comparison
Concentrations
25
Analyzer 1 Analyzer 2
20
NH3 (ppb)
15
10
5
0
Hour DOY
0
12 206
0
12 207
0
12 208
0
12 209
0
12 210
0
12 211
0
Methods: Instrument Comparison
Gradients
3
DOY 209
Analyzer 2 NH3 Gradient (ppb)
2
1:1
1
0 -3 -2 -1 -1 0 1 2 3
-2
-3
Analyzer 1 NH3 Gradient (ppb)
Methods: NH3 Gradients
2002 Soybean
100 90 80
Cumulative Percent
70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Ratio of Gradient to Detection Limit
85% of gradients were > detection limit N = 2771
Results: Hourly NH3 Concentrations
2002 Soybean
6
5
P 4 e r c 3 e n t 2
1
0 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45
NH 3 (ug m -3 )
Results: NH3 Gradients and Fluxes
2002 Soybean
NH3 gradient and flux - DOY 194
1 0.5 0.1
NH3 Gradient (ug/m3)
0.05 -0.5 -1 -1.5 -2 -0.1 -2.5 -3 Hour NH3grad NH3 flux -0.15 -0.05 0 5 10 15 20 25 0
Net flux = -12 ng NH3-N/m2/s Vd = -0.35 cm/s
NH3 flux (ug/m2/s)
0
Ammonia Concentrations Within the Vicinity of a Swine Production Facility
• Objectives:
Measurement of horizontal NH3 gradients around a swine production facility from the housing/lagoon complex to 500 m. Estimation of NH3 dry deposition using the resistance approach (Fowler et al., 1998) and Gaussian modeling.
Development of a mass balance using measured emissions (Harris et al., 2001).
NH3
NH4+
Site Layout
N
NH3 Sampler Met. Station
Lagoon
Hog House
500 m
Methods
[NH3] = Q/V
Q = Mass of NH3 adsorbed V = Volume of air sampled
Sutton et al., 2001
Q = (ce – cb)v
Ce – Measured NH3 concentration Cb – Blank value V – Extract volume (2.5 ml)
V = D•A•t/L
D – Diffusion coefficient A – Area of adsorbing surface t – Duration of exposure (1 week) L – Length of diffusion path (35 mm)
Methods
• Deposition
FNH3 = [NH3]•Vd
Vd = 1/(Ra + Rb + Rc)
Rc will be calculated using the relationship between Rc and [NH3] (Fowler et al., 1998) and Gaussian modeling.
Rb
Ra
Rb = (2/(ku*))(Sc/Pr)2/3
Ra = U/(u*)2
u* is determined using velocity profile (crops) and eddy covariance (forest) approaches
Methods
• Calibrate using NH3 standard in flow-through chamber and by comparison with annular denuder.
Results
• Measurements began April 2003
• Median C.V. = 6.4% (N = 236)
• Mean Blank = 2.7 g NH3 m-3 (N = 86)
NH3
NH4+
Results
400 375 350 325 300 275 250 O 225 O 200 O 175 150 125 O 100 O 75 O O 50 O O O 25 0 0 2 5 5 0 7 5
Extensions represent 95% C.I. for mean concentration.
NH3 (ug m -3 )
O
O O
O O O O O O O O
O
1 0 0
1 2 5
1 5 0
1 7 5
2 0 0
2 2 5
2 5 0
2 7 5
3 0 0
3 2 5
3 5 0
3 7 5
4 0 0
4 2 5
4 5 0
Distance from House/Lagoon (m)
Summary
• Annular Denuder
– Multiple analytes, selective, well documented – Integrated sample, labor intensive, relatively expensive
• Chemiluminescence
– Good temporal resolution, easily calibrated, relatively inexpensive – Aerosol interference
• Passive Denuder
– Inexpensive, allows greater spatial resolution, selective – Single analyte, integrated sample, requires calibration
NH3 NH4+
Acknowledgements
• North Carolina Division of Air Quality, North Carolina Pork Council, National Pork Producers Council, and North Carolina Water Resources Research Institute. • Wayne Fowler (U.S. EPA), Lynette Mathis (North Carolina State University), Mark Barnes (North Carolina State University), and Brad Hendrickson (UNC-CH IMS).
NH3
NH4+