Measurement of Ammonia Fluxes at a Cattle Feedlot Using Relaxed Eddy Accumulation

Patrick O’Keeffe

Shelley PressleyEugene AllwineBrian Lamb

Kris JohnsonJennifer MichalSarah Spogen

MotivationNH3 impacts:

• atmosphere - major contributor to secondary aerosol formation

• aquatic ecosystems - deposition can lead to eutrophication

Atmospheric NH3 Sources • livestock operations,

fertilizer/soils, wastewater treatment facilities, industrial sources, mobile sources

Ammonia in our air

Global budget for NH3

Source Amount Tg/yr

Agricultural (livestock, fertilizers, crops) 37.4 (65%)

Natural or biogenic (oceans, undisturbed soils, animals)

10.7 (19%)

Biomass burning 6.4 (11%)

Other (industrial, wastewater facilities, fossil fuel combustion, mobile sources)

3.1 (5%)

Total 57.6

Why at a feedlot?

• Recent requirements under EPA mandate all CAFO’s (>1000 hd) must report NH3 and H2S emissions under the Emergency Planning and Community Right to Know Act (EPCRA)

• Because no officially adopted emission factors are currently available to use for this purpose, the final rule allows reports to reflect “good faith estimates.” - users are provided a worksheet

Simple emission estimates using a worksheet

The field campaign

• Mid-sized cattle feedlot (30,000 head)

• Mid-west feedlot containing growing and finishing steers

• Measurements conducted during two weeks in spring– Cooler temperatures; periodic rainfall; dusty

• Techniques: relaxed eddy accumulation (REA), ultraviolet DOAS, horizontal profiling system and mobile van outfitted with various instruments

Measurement SiteInstrumentation

location

Mobile Vanroute

Feed Storage

Manure Compost

N

Predominant Winds (either SW or SE)

DOAS• Differential Optical Absorption Spectrometer

• NH3 concentrations measured via Beer’s law

Short path (110m)

line-averaged

200-240 nm wavelength

TGAPS• Trace Gas Analytical Profiling System

• N2O analyzed with GC-electron capture detector (ECD) technique• Same path as DOAS, time-averaged N2O concentrations• 7 inlets, runs continuously, 5 min avg. DOAS

Retro-reflectors

TGAPSSamplinglines

Mobile Van• Mobile Van

• Stationary or mobile sampling for• CO2, CH4, NH3, NO, NO2

• Mobile transects (line-averaging) or fixed time series

REA Relaxed Eddy Accumulation

TGAPS inlets

3D SonicAnemometerREA system

REA is a micrometeorological flux measurement technique, in this case used for NH3 flux measurements

REA Method• High frequency sampling of wind with time averaged

NH3 concentrations

• Up and down wind gusts are conditionally sampled through honeycomb denuders

• Denuders capture NH3 over 1 hr period and air volume sampled is known

• Colorimetric analysis used to determine NH3 conc.

• Fluxes calculated with mean ‘up’ and ‘down’ concentrations of NH3 and standard deviation of wind speed ( )−+ −= CCF wβσ

3D sonic Anemometer

CO2/H2O Analyzer

Thermo ScientificHoneycomb Denuders

REA NH3 system

Results

• REA NH3 Fluxes collected over 4 days

• Wind directions dictate which portion of the feedlot was sampled

• Footprint lengths important, primarily dependent on stability of the atmosphere

• Operational parameters also important –still working to incorporate this data

Run 11: evening E-SE winds

Light winds, evening time, temperatures ~20 C

NH3 flux = 105 µg/m2s

Run 13: mid-day, S-SW winds

higher winds, mid-day, temperatures ~25 C

NH3 flux = 253 µg/m2s

Run 14: mid-day, S-SW winds

Note – not to scale

Meterological Conditions - April 23

0

5

10

15

20

25

30

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

Tem

pera

ture

(C)

0

1

2

3

4

5

6

Win

d Sp

eed

(m/s

)temperaturewind speed

higher winds, mid-day, temperatures ~25 C

NH3 flux = 352 µg/m2s

Run 11

Runs 13-14

Summary• NH3 fluxes during warm spring conditions

averaged 142±87 µg/m2s

• Emissions were from an upwind fetch of ~100 m which typically encompassed 225 hd of 400 kg growing and finishing steers.

• Acknowledgements– USDA for research funding

– Jay Ham, Colorado State, for help developing REA

– CAFO’s for allowing us to make measurements

Future Work

• Further refine the REA results • Look at turbulence/atmospheric stability

parameters

• Calculate footprint size for each run

• Use WindTrax – atmospheric dispersion model• Determine NH3 fluxes using WindTrax and DOAS

for comparison with REA results

• Integrate results with other datasets (i.e. feedlot operations, additional measurements)