United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-02/017 May 2002
Review of Emission Factors and
Methodologies to
Ammonia Emissions from Animal
Handling
Michiel R. J. Doom, David F. Natschke, and PieterC. Meeuwissen
The report summarizes and dis-
cusses recent available U.S. and Euro-
pean information on ammonia (NH3)
emissions from swine farms and as-
sesses its applicability for general use
in the U.S., particularly in North Caro-
lina. The emission rates for the barns
calculated by various methods show
good agreement and suggest that the
barns are a more significant source
than previously thought. A general emis-
sion factor for barns of 3.7 ± 1.0 kg
NH3/year/finisher pig (or 59 ± 10 g NH3/
kg live weight/year) is recommended,
based on the results of multiple field
tests. For lagoons, it was found that
there is good similarity between the field
test results and the number calculated
by a mass balance method. The sug-
gested annual NH3 emission factor for
swine farm lagoons in North Carolina is
2.4 kg/year/pig. The emission factor for
lagoons, based on field tests at only
one lagoon, is considered to be less
accurate than that for barns. Emission
rates from sprayfields were estimated
using a total mass balance approach,
while subtracting the barn and lagoon
emissions.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
In the U.S., the atmospheric deposition
of ammonia (NH3) and other nitrogen com-
pounds has received renewed attention
as a major route of entry into watersheds,
especially the lower river basins and
coastal estuaries of the eastern U.S. At-
mospheric NH3 also contributes to the
formation of fine particulate matter by re-
acting with acid gases from combustion
sources. The most significant source of
NH3 emissions (about 80%) in the U.S. is
livestock waste. An increasing tendency
toward industrialization of farming prac-
tices in the U.S. over the last two de-
cades has resulted in increased farm size
and confinement of animals. For example,
in 1991, the average swine population in
North Carolina was about 4.5 million, and
the number had increased to about 10
million by 1997. To better understand NH3
emissions from large swine farms, the
State of North Carolina coordinated a sig-
nificant test effort during the late 1990s.
Initially, this program focused on the waste
storage lagoons because they were be-
lieved to be the major source of NH3.
Later, the focus shifted toward emissions
from barns. Field tests and field test re-
sults are summarized in the report, as well
as a comprehensive mass balance ap-
proach and supporting information from the
European and U.S. scientific literature.
Dutch and Danish NH3 emission meth-
odologies follow a mass balance ap-
proach based on the average yearly
nitrogen excretion per animal type and
the different emission or volatilization fac-
-------
tors from specific emission sources; i.e.,
barn, storage/treatment, and land appli-
cation. This approach takes into account
the entire waste management pathway.
There are general limitations to a nitro-
gen mass balance approach. Inaccura-
cies in the determination of the nitrogen
content of manure or litter can lead to
inaccuracies in estimates of NH3 losses.
Another limitation of the mass balance
method is that it is not equipped to ad-
dress the loop that is induced by the use
of NH3-laden lagoon water to flush and
fill the pit under barns, as occurs in North
Carolina pull-plug barns. However, the
approach may be appropriate for a flush-
type farm. The method may also be use-
ful as an emission estimation tool in
discussions regarding the closing of la-
goons and alternative waste treatment
methods.
Field Tests In North Carolina
Comprehensive field tests were con-
ducted in the mid to late 1990s at a swine
operation in Eastern North Carolina (Farm
10). The test program at Farm 10 was
coordinated by the North Carolina De-
partment of Environment and Natural Re-
sources (NCDENR) and included
research teams from or funded by
NCDENR, the U.S. Department of Agri-
culture (USDA), U.S. EPA's Air Pollution
Prevention and Control Division (APPCD),
North Carolina State University, and the
University of North Carolina at Chapel
Hill. Farm 10 is an integrated farrow-to-
finish farm with nine finishing barns and
four farrowing barns. The waste manage-
ment system is "flush-type" with a pit un-
der each side of the barn running the
length of the barn. Each pit (per half barn)
is flushed every week (assumed) for sev-
eral hours with water from the lagoon.
After flushing, no water remains in the
pits. This type of waste removal system is
uncommon, because most farms now
have a pull-plug system. At the time of
the tests, the total swine population at
Farm 10 consisted of 7,480 finishers, 1,212
sows and boars, and 1,410 piglets; aver-
age weights were 135 Ib (61.4 kg), 400 Ib
(181.8 kg), and 25 Ib (11.4 kg), respec-
tively. The Farm 10 total live weight was
1,529,850 Ib (695,386 kg), and the aver-
age animal weight was 151 Ib (69 kg).
Barns
A coarse NH3 average emission factor
of 9.9 g/pig/day was reported for several
swine barns at Farm 10 in North Caro-
lina. On an annual basis, these emis-
sions are presented as 3.69 kg/pig/year
with an individual seasonal range of 2.74
- 4.75 kg/pig/year. Note that the values
presented for Farm 10 are described as
an "upper bound," since data were col-
lected only during the daytime.
Follow-up field tests were conducted at
four separate feeder-to-finish farms in
southern North Carolina in 2000. Each
farm consisted of 10 tunnel-ventilated
barns with a pull-plug waste removal sys-
tem. Three barns at each farm were tested,
representing young, middle, and older age
groups within the production cycle. Pre-
liminary conclusions indicate that there is
no statistically significant variation in the
emission factor as a function of age or
weight. The most likely explanation for
this is that the recycled lagoon water used
to flush the pit below the barn floor pro-
vides a baseline emission source that
contributes a significant portion of the barn
emissions. Also, it is noted that there is a
significant diurnal cycle. Based on these
field tests, a preliminary emission factor
of 4.31 kg/pig/year is suggested for emis-
sions in the summer from pull-plug,
feeder-to-finish operations.
Lagoons
The lagoon at Farm 10 was sampled
by several research groups over a period
of a year using different techniques. One
group used a flux chamber method to
measure NH3 emissions from the lagoon
surface. The NH3 was converted to nitric
oxide which, in turn, was measured using
a chemiluminescence technique. A mi-
crometeorology method was used by an-
other group. This technique uses a vertical
array of wind speed and temperature sen-
sors operated with the air sampling oc-
curring in parallel. During testing, this
vertical array is floated to the middle of
the lagoon. Ammonia concentrations were
obtained by drawing unfiltered air through
gas-washing bottles containing sulfuric
acid at a known rate for 4 hours. The
resulting ammonium (NH4+) concentra-
tions were analyzed using colorimetry.
Test results are summarized in Table 1.
Spraying Operations
Effluent from the lagoon is sprayed on
surrounding crop fields. Unfortunately, no
NH3 emissions from spraying operations
were measured for Farm 10; however,
one Georgia field study was found that
pertains to NH3 emissions from spray-
fields. A micrometerology method was
used to determine NH3 emissions from a
sprayed oats field of 12 hectares in Geor-
gia. To this field, 45 kg total N per hectare
was applied, of which 4.7 and 20.3 kg
volatilized during application and post-
application, respectively. This translates
into a volatilization factor of 56%. Ammo-
nia volatilization from land application of
pig slurry in France was estimated to be
between 37 and 63% of ammoniacal ni-
trogen. Another source reported an even
greater range for NH3 losses from land
application of pig waste, 11 to 78% am-
moniacal nitrogen.
Discussion
To date, the most complete U.S. data
set of NH3 emissions based on field mea-
surements from a full-scale swine farm is
that of North Carolina Farm 10. The Farm
10 emission estimates can be compared
with estimates based on the mass bal-
ance method. Because finishing pigs are
the most significant sub-source category,
and only emissions from finishing pig
barns were collected at Farm 10, the fin-
isher pig population was used as a base
for the comparisons. No field tests were
conducted at the farm's sprayfields, but
an attempt was made to estimate these
emissions based on volatilization percent-
ages from the literature.
Table 2 summarizes NH3 emission
rates from barns, lagoon, and sprayfield
for Farm 10, as well as rates calculated
by a mass balance. The emission rates
for the barns in Table 2 show good agree-
ment and suggest that the barns are a
more significant source than previously
thought. The emission rate for barns from
the mass balance approach is somewhat
lower than those of the field tests, but this
may be due to the low volatilization per-
centage that was used in the mass bal-
ance computation (15%). It is believed
that there is enough evidence to recom-
mend an emission factor for average fin-
isher pigs of 3.7 ± 1.0 kg NH3/year/pig
(59 ± 10 g NH3/kg live weight/year). This
value is supported by the 4.3 kg NH3/
year/finisher pig reported for the summer.
There is surprising similarity between
the field test results for the lagoon (aver-
age 49 kg/day) with the number calcu-
lated by the mass balance method, which
was 52 kg/day. Consequently, the sug-
gested annual emission factor for NH3
emissions from a swine farm lagoon in
North Carolina becomes 26 g/kg live
weight/year. This lagoon emission factor
does not take vacancy and mortality into
account, nor does it address differences
in lagoon characteristics (e.g., pH) or cli-
matological factors (e.g., temperature, rain,
and wind). Additional study of lagoons
aimed at enhancing understanding of ni-
trogen pathways (e.g., to sludge or to N2)
will assist in further developing a com-
prehensive mass balance.
By applying the simple mass balance
method, sprayfield emissions at Farm 10
were estimated at 19 kg/day (6,950 kg
per year). This reflects emissions only
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Table 1. Results from Ammonia Emission Field Tests at Lagoons at Two NC Swine
Farms
Field Test
Method
Flux
Chamber
Micro-
meteorology
Farm
No.
10
10
10
10
10
10
10
10
10
10
Study Period
Aug. 1997
Dec. 1997
Feb. 1997
May 1 998
Average
Spring 1997 to
Winter 1998
Spring 1997
Summer 1997
Winter 1998
Average
NH3per
Lagoon
(kg/day)
156.2
32.8
11.9
66.3
66.8
28.1
26.0
50.5
20.5
31.3
NH3per
Animal
(kg/ani./yr)
5.64
1.19
0.43
2.40
2.42
0.75
0.94
1.82
0.74
1.06
NH3per
Standard
Live Weight
(kg/kg/yr)
0.0821
0.0172
0.0062
0.0349
0.0351
0.0133
0.0137
0.0265
0.0107
0.0161
Table 2. Summary of Farm 10 Emissions Data
Source
Barns/lagoon/sprayfield
Barns
Barns
Barns
Barns
Barns
Barns
Lagoon
Lagoon
Lagoon
Lagoon
Lagoon
Sprayfields
Activity
Finishers only
All pigs
Finishers only
Finishers only
Finishers only
Finishers
Generic pigs
All pigs
All pigs
All pigs
All pigs
Finishers only
Finishers only
Emissions
kg/day
143
64
43
76
56
33-69
64
52
67
31
49
33
19
Method
Mass balance
Mass balance
Mass balance
OP-FTIR" field test
Field test
Literature, Europe
Literature, Canada
Mass balance
Flux chamber field test
Micrometeorology field test
Average of 2 field tests
Average of 2 field tests
Mass balance
"Open-path Fourier Transform Infrared
from finishers (61.4 kg). As indicated ear-
lier, this number constitutes a rough guess.
The calculations in this section suggest
that sprayfield operations are a small but
significant fraction of total farm emissions.
But, since spraying is limited to certain
seasons and certain hours of the day, it is
likely that these spray operations are quite
significant during the actual events.
Conclusion
The total of emissions for finishing pigs
from barns (76 kg/day), lagoon (33 kg/
day), and assumed spray application (19
kg/day) is 128 kg/day (or 102 g NH3/kg
live weight/year). The 128 kg/day number
compares well to the number established
by the simple total mass balance (143 kg/
day). Therefore, it can be concluded that
a mass balance approach can be useful
in estimating NH3 emissions from swine
farms, especially those that do not em-
ploy pull-plug waste flushing technology.
The average weight of the swine at
Farm 10 is 69 kg. If we assume that this
swine population reflects a self-sustain-
ing population (i.e., is similar to the aver-
age swine population in North Carolina),
we can arrive at an emission factor of 7
kg NH3/animal/year (using the 102 g NH3/
kg live weight/year number). This emis-
sion factor is a generic emission factor
based mainly on field data for two farms
in North Carolina for barns and one farm
for lagoons. The sprayfield component
was calculated using a simple mass bal-
ance approach based on nitrogen feed
intake. This emission factor is comparable
to other generic emission factors from the
literature (see Table 3). The three Euro-
pean emission factors in Table 3 are all
somewhat lower than the North Carolina
emission factor. The difference may be a
result of numerous factors, including (but
not limited to) different animal waste han-
dling practices (use of lagoons and flush-
ing with lagoon water as opposed to pits)
and lower average ambient temperatures.
If we take the 1997 emission factor (5 kg/
animal/year) as a lower boundary, we
may possibly suggest a range for the
North Carolina emission factor of ± 2 kg/
animal/year.
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Table 3. Comparison of Ammonia
Source
1992 Report
1997 Report
1998 EMEP/CORINAIR
1994 Report
This Report"
NH3
Emission Factors for Swine
Emission Factor (kg/animal/yr
5
5
6
9b
7±2
"Number now believed to be biased high, apparently due to earlier
interpretation error
bBased on limited field tests and theoretical sprayfield emissions
estimation
M. Doom and D. Natschke are with ARCADIS Geraghty & Miller, Durham, NC, and
P. Meeuwissen is with ARCADIS, Arnhem, The Netherlands.
Susan A. Thorneloe is the EPA Project Officer (see below).
The complete report, entitled "Review of Emission Factors and Methodologies to
Estimate Ammonia Emissions from Animal Waste Handling," will be available at
http://www.epa.gov/ORD/NRMRUPubs or as Order No. PB2002-105708; Cost:
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The EPA Project Officer can be contacted at:
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