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: 2000
Sites County-Scale Emission Density
(kg NH3 km-2)
Clinton 4800
Kinston 2280
Morehead City 320
NH3 NH4+
2000 County-Scale NH3 Emissions (CMU V2.0)
*
* *
5000 N
Methods
Teflon Filter Pack
Contains Teflon and nylon Filters
capture fine particulates containing
ammonium and other species.
Denuder Tube
Concentric cylinders of etched glass are
coated with citric acid. NH3 molecules are
AIR FLOW
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.
Cyclone
Stops particulates >2.5 m in size from
Air entering annular denuder system.
Intake
Schematic of assembled annular denuder system
Results: Annual Concentrations
6 \\\ Clinton
xx Kinston
// Morehead City
5
4
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
10 Kinston
9 Spring/Summer
0.8 8
7
Percent
6
0.7 5
4
3
2
NH3/(NH3 + NH4+)
0.6 1
0
0.5 0 90 180 270 360
Wind Direction
0.4
9 Kinston
8 Fall/Winter
0.3 7
6
Percent
5
0.2 4
3
2
0.1 1
0
0.0 0 90 180 270 360
W Sp Su F W Sp Su F W Sp Su F Wind Direction
Clinton Kinston Morehead City
Results: Inorganic PM2.5
10
SO 4=
9
NO 3-
8
NH 4+
7
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
400
Excess NH 3 (nmol m -3)
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-gas-
limited 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
y = momentum (u), heat (), mass (c)
dy
K-theory Fy K y
dz
In this case, y = H2Ov, CO2, and
Modified Bowen-ratio
dNH 3
FNH 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 Upper Inlet
Configuration
Heated Sample Line
8.5 Lpm
Solenoid Valve
6.2 m
Mobile Lab
NH3 Analyzer
Lower Inlet
Nt Converter
11.4 m
Methods: Chemiluminescence
NOx
PMT
Inlet Nt Converter Nt NOx Converter
NO
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
5
%CV (15 Min. Ave.)
4
y = 8.084x-0.5231
3 2
R = 0.9023
2
-0.9058
y = 17.331x
1 2
R = 0.9505
0
0 10 20 30 40
NH3 (ppb)
Converter 1 Converter 2 Power (Converter 1) Power (Converter 2)
0.76
NH 3H 1 NH 3H 2
D.L.(%Diff .) 13.1
2
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
8
NH3 (ppb)
6
4
2
0
-2
0 50 100 150 200 250 300
Seconds
Methods: Instrument Comparison
Concentrations
25
Analyzer 1
Analyzer 2
20
15
NH3 (ppb)
10
5
0
Hour 0 12 0 12 0 12 0 12 0 12 0 12 0
DOY 206 207 208 209 210 211
Methods: Instrument Comparison
Gradients
3
DOY 209
Analyzer 2 NH3 Gradient (ppb)
2
1:1
1
0
-3 -2 -1 0 1 2 3
-1
-2
-3
Analyzer 1 NH3 Gradient (ppb)
Methods: NH3 Gradients
2002 Soybean
100
90
80
70
Cumulative Percent
60
85% of gradients were > detection limit
50 N = 2771
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Ratio of Gradient to Detection Limit
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 0.1
0.5
0.05
NH3 Gradient (ug/m3)
0
NH3 flux (ug/m2/s)
0 5 10 15 20 25
-0.5 0
-1
-1.5 -0.05
-2
-0.1
-2.5
-3 -0.15
Hour
NH3grad NH3 flux
Net flux = -12 ng NH3-N/m2/s
Vd = -0.35 cm/s
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 Rb = (2/(ku*))(Sc/Pr)2/3
Ra 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 Extensions represent 95% C.I. for mean concentration.
350
325
300
275
NH3 (ug m -3 )
250 O
225
O
200 O
175
150
125 O
100 O O
75 O O O
O
50 O O
OO O O
25 O
O
O O
O O
0
0 2 5 7 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4
5 0 5 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5
0 5 0 5 0 5 0 5 0 5 0 5 0 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+