Measurement of Ammonia Concentrations and Fluxes: Recent Examples Using Denuder and

Chemiluminescence Technologies

 

John WalkerU.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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High Priority Research Areas

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 RobargeNorth Carolina State University, Department of Soil Science, Raleigh, NC 27695

Dave R. WhitallCenter for Coastal Monitoring and Assessment, NOAA, Silver Spring, MD 20910

Hans W. PaerlUniversity 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, SO4

2-, 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+

Emission Density(kg NH

3km-2)

2000 County-Scale NH3Emissions (CMU V2.0)

< 500500 to 750750 to 10001000 to 15001500 to 20002000 to 30003000 to 5000> 5000

**

*

Morehead CityKinstonClinton

N

Teflon Filter PackContains Teflon and nylon Filters

capture fine particulates containing ammonium and other species.

Denuder TubeConcentric cylinders of etched glass are coated with citric acid. NH3 molecules are

retained in this section.

Denuder TubeConcentric cylinders of etched glass are

coated with sodium carbonate (base). Acid molecules (HCl, HONO, HNO3, SO2)

are retained in this section.

CycloneStops particulates >2.5 m in size from

entering annular denuder system.

AIR

FL

OW

AirIntake

Schematic of assembled annular denuder system

Methods

Results: Annual Concentrationsu

g m

-3

NH3 SO2 HNO3 HONO HCl NH4+ NO3

- SO4= Cl

-

-------------------------Gas --------------------------- --------------Aerosol --------------

\\\ Clintonxx Kinston// Morehead City

0

1

2

3

4

5

6

Results: Ammonia/Ammonium FractionationN

H3/(

NH

3+

NH

4+)

Clinton Kinston Morehead City

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

W Sp Su F W Sp Su F W Sp Su FP

erce

nt

Wind Direction

KinstonSpring/Summer

0123456789

10

0 90 180 270 360

Per

cent

Wind Direction

KinstonFall/Winter

0123456789

0 90 180 270 360

Results: Inorganic PM2.5ug

m-3

Cl -

NH4+

NO3-

SO4=

Clinton Kinston Morehead City

0

1

2

3

4

5

6

7

8

9

10

W Sp Su F W Sp Su F W Sp Su F

Results: Aerosol Formation

HClClHNONOSONHNHNH Excess 3 33443 2

Exc

ess

NH

3(n

mol

m-3

)

Clinton Kinston Morehead City

-50

0

50

100

150

200

250

300

350

400

450

500

W Sp Su F W Sp Su F W Sp Su F

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

ywFy

dz

dyKF yy

Eddy Covariance

K-theory

y = momentum (u), heat (), mass (c)

In this case, y = H2Ov, CO2, and

Modified Bowen-ratio

dz

dNHKF yNH

33

NH3 NH4+

Methods: Equipment

NH3 flux tower - Duplin Co., NC

NH3 gradient – Chemiluminescence

CO2/H2O gradient – LI6262

Temperature gradient – Thermocouple

Eddy Covariance CO2/H2O/Heat fluxes - LI7500/Gill Windmaster Pro

Inlet Heights – 1 and 6m15 min. switching timeHeated sample linesHourly gradients

Hourly - RH PAR/Net radiation Rainfall Soil volumetric water Soil heat flux

Weekly - LAI Leaf total N Soil extractable NH4

+/NO3-

Solenoid Valve

Mobile Lab

Lower Inlet

Upper Inlet

Heated Sample Line8.5 Lpm

Nt Converter

NH3 Analyzer

Methods: Tower NH3 Configuration

6.2 m

11.4 m

Methods: Chemiluminescence

Routine calibration with NO standard

Converter efficiency test with NH3 standardConverter efficiency typically 65 – 85%

Inlet

Nt Converter ModuleNH3/NOx/NO Analyzer

Nt ConverterNOx Converter

Rx Cell

PMT

Nt converter at 825 oC converts NHx + NOx to NONOx converter at 325 oC converts NOx to NO

Nt

NOx

NO

NH3 NH4+

Analyzer Precision

y = 17.331x-0.9058

R2 = 0.9505

y = 8.084x-0.5231

R2 = 0.9023

0

1

2

3

4

5

6

0 10 20 30 40

NH3 (ppb)

%C

V (

15

Min

. Av

e.)

Converter 1 Converter 2 Power (Converter 1) Power (Converter 2)

Methods: Gradient Detection Limit

76.0

33

21.13.).(%. 21

HH

NHNHDiffLD

Zero Air Off at Tower Inlet

-5

0

5

10

15

20

25

0 50 100 150 200 250 300

Seconds

NH

3 (p

pb)

Zero Air On at Tower Inlet

-2

0

2

4

6

8

10

12

0 50 100 150 200 250 300

Seconds

NH

3 (

pp

b)

Methods: Response Time

0

5

10

15

20

25

NH

3 (p

pb

)

Analyzer 1

Analyzer 2

1212 121212120 00 000 0

207206 210209208 211

Hour

DOY

Methods: Instrument Comparison Concentrations

-3

-2

-1

0

1

2

3

-3 -2 -1 0 1 2 3

Analyzer 1 NH3 Gradient (ppb)

An

aly

zer

2 N

H 3 G

rad

ien

t (p

pb

)Methods: Instrument ComparisonGradients

1:1

DOY 209

Methods: NH3 Gradients2002 Soybean

Cum

ulat

ive

Per

cent

0

10

20

30

40

50

60

70

80

90

100

Ratio of Gradient to Detection Limit

0 10 20 30 40 50 60 70 80 90 100

85% of gradients were > detection limitN = 2771

Results: Hourly NH3 Concentrations2002 Soybean

NH 3 (ug m -3)

Percent

0

1

2

3

4

5

6

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

Results: NH3 Gradients and Fluxes2002 Soybean

NH3 gradient and flux - DOY 194

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

0 5 10 15 20 25

Hour

NH

3 G

rad

ien

t (u

g/m

3)

-0.15

-0.1

-0.05

0

0.05

0.1

NH

3 f

lux

(ug

/m2/s

)

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+

500 m

NNH3 Sampler

Met. Station

Lagoon

Hog House

Site Layout

Methods

Q = (ce – cb)vCe – Measured NH3 concentrationCb – Blank valueV – Extract volume (2.5 ml)

[NH3] = Q/V

V = D•A•t/LD – Diffusion coefficientA – Area of adsorbing surface t – Duration of exposure (1 week)

L – Length of diffusion path (35 mm)

Q = Mass of NH3 adsorbed

V = Volume of air sampled

Sutton et al., 2001

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

Results

• Measurements began April 2003

• Median C.V. = 6.4% (N = 236)

• Mean Blank = 2.7 g NH3 m-3 (N = 86)

NH3 NH4+

Methods

• Calibrate using NH3 standard in flow-through chamber and by comparison with annular denuder.

NH

3(u

g m

-3)

0255075

100125150175200225250275300325350375400

Distance from House/Lagoon (m)

0 25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

OO

O

OO

OO

OOO

O

O

O O

OO

O

OOO

OO

Results

Extensions represent 95% C.I. for mean concentration.

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+