1656

Ammonia and hydrogen sulfide emissions from swine production facilities in North America: A meta-analysis1

Z. Liu,*2 W. Powers,† J. Murphy,* and R. Maghirang*

*Department of Biological and Agricultural Engineering, Kansas State University, Manhattan 55506; and †Department of Animal Science and Biosystems and Department of Agricultural Engineering, Michigan State University, East Lansing 48824

AbstRAct: Literature on NH3 and H2S emissions from swine production facilities in North America was reviewed, and a meta-analysis was conducted on mea-sured emissions data from swine houses and manure stor-age facilities as well as concentration data in the vicinity of swine production facilities. Results from more than 80 studies were compiled with results from the 11 swine sites in the National Air Emissions Monitoring Study (NAEMS). Data across studies were analyzed statisti-cally using the MIXED procedures of SAS. The median emission rates from swine houses across various produc-tion stages and manure handling systems were 2.78 and 0.09 kg/yr per pig for NH3 and H2S, respectively. The median emission rates from swine storage facilities were 2.08 and 0.20 kg/yr per pig for NH3 and H2S, respective-ly. The size of swine farm that may trigger the need to report NH3 emissions under the Emergency Planning and Community Right-to-Know Act (EPCRA) is 3,410 pigs on the basis of the median NH3 emission rate (4.86 kg/yr per pig), but the threshold can be as low as 992 pigs on the basis of the 90th-percentile emission rates (16.71 kg/yr per pig). Swine hoop houses had significantly higher NH3

emission rate (14.80 kg/yr per pig) than other manure-handling systems (P < 0.01), whereas deep-pit houses had the highest H2S emission rate (16.03 kg/yr per pig, P = 0.03). Farrowing houses had the highest H2S emission rate (2.50 kg/yr per pig), followed by gestation houses, and finishing houses had the lowest H2S emission rate (P < 0.01). Regression models for NH3 and H2S emission rates were developed for finishing houses with deep pits, recharge pits, and lagoons. The NH3 emission rates in-creased with increasing air temperature, but effects of air temperature on H2S emission rates were not significant. The recharge interval of manure pits significantly affected H2S but not NH3 emission rates. The H2S emission rates were also influenced by the size of the operation. Although NH3 and H2S concentrations at the edge of swine houses or lagoons were often higher than corresponding acute or intermediate minimum risk levels (MRL), they decreased quickly to less than corresponding chronic or intermedi-ate MRL as distances from emission sources increased. At the distances 30 to 1,185 m from emission sources, the average ambient concentrations for NH3 and H2S were 46 ± 46 µg/m3 and 4.3 ± 8.6 µg/m3 respectively.

Key words: ammonia, emission, hydrogen sulfide, manure, meta-analysis, swine

© 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2014.92:1656–1665 doi:10.2527/jas2013-7160

INtRoductIoN

Air emissions from swine production facilities have received considerable attention because of hu-man health and environmental implications. The major farm emissions of interest include ammonia (NH3) and hydrogen sulfide (H2S). Hydrogen sulfide is of inter-

est mainly at the local level because of health concerns, whereas NH3 has regional-scale impacts on ecosys-tems (NRC, 2003). Air emissions from industries are subject to permitting requirements under the Clean Air Act (cAA) as well as reporting requirements under the Emergency Planning and Community Right-to-Know Act (EPcRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (cERcLA) if emissions reach specified thresholds; for example, op-erations that exceed 45.4 kg/d (100 lb/d) NH3 or H2S emissions are required to report under EPCRA. Accurate quantification of farm emissions is essential to ensure compliance with the regulatory requirements, but direct

1Funding for this work was provided by the National Pork Board (NPB) Project 12-002. This is contribution 14-083-J from the Kansas Agricultural Experiment Station.

2Corresponding author: zifeiliu@ksu.eduReceived September 17, 2013.Accepted January 8, 2014.

Published November 24, 2014

Ammonia and hydrogen sulfide emissions from swine facilities 1657

measurements of farm emissions are expensive and dif-ficult. Fortunately, a large volume of published studies on NH3 and H2S emissions from swine production facilities are available for a meta-analysis. Meta-analysis is a quan-titative statistical analysis of a collection of results from individual previous studies for the purpose of integrating the findings. Results from meta-analyses are usually more robust and have less bias than individual studies because of improved statistical power (Cohn and Becker, 2003; Garg et al., 2008).

The objective of this study was to review published lit-erature on NH3 and H2S emissions from swine production facilities in North America and to conduct a meta-analysis that integrates results of independent studies. Measured emissions data from both swine houses and manure stor-age facilities as well as concentration data in the vicinity of swine production facilities were included in the study.

MAtERIALs ANd MEthods

Literature Search and Data ExtractionMultiple strategies were undertaken to identify poten-

tially eligible studies to be included in the meta-analysis. The inclusion criteria were that studies must have been con-ducted in North America and must have reported measured NH3 or H2S emission data from swine production facilities, including manure storage systems, or concentration data in the vicinity of swine facilities. Data from reports of the 11 swine sites in the National Air Emissions Monitoring Study (NAEMs) were included in the database. Two individuals independently conducted the search processes and screened the studies by reading the title and abstract to select studies for full review according to the inclusion criteria.

The included studies were distributed to a group of 7 trained analysts for data extraction. Standard data ex-traction sheets were developed for consistency. Emission data were extracted following the protocol presented in Table 1. Some studies provided emission data from differ-ent sites or under different settings; in these cases, more than 1 data point was extracted from 1 study. Each study was reviewed in duplicate by 2 individual analysts for quality control. The author met with all analysts regularly to address issues during the data extraction process. Data quality was checked and disagreements were resolved by consensus between the analysts or by the author. After the data extraction spreadsheets were completed by the group of analysts, 1 of the analysts synthesized the completed data extraction spreadsheets from different analysts, and the process was reviewed by the authors. As a result of the data review and extraction processes, a meta-analysis da-tabase was created. Emission data for NH3 and H2S were compiled into the 2 emission sources (swine houses and manure storage facilities). Air concentration data were

compiled separately and included sampling locations and distances from emission sources.

Data Analysis

Various units of emission data were used in the literature. To perform statistical analysis and to compare the emission data between different studies, the units of measured emis-sion data were converted to kilograms per year per pig and kilograms per year per AU (Au is an animal unit corre-sponding to 500 kg body mass) for emissions from swine houses and to kilograms per year per pig and kilograms per year per square meter for emissions from manure storage fa-

table 1. Emission data extraction protocolCategories of data Extracted valuesInformation on the paper

Name of authors Input the textYear of publication Input numeric valuesTitle of the study Input the text

Information on emission sourcesEmission source type Type of swine house manure systems:

select from deep pit, dry,1 hoop, drain pit, or recharge pit with frequency re-corded; type of manure storage facilities: select from lagoon or slurry storage

Stage of production Select from gestation, farrowing, nurs-ery, and finishing

Ventilation type Select from mechanical and naturalSize of operation Input number of animalsAverage pig weight Input numeric values (kg)Area of manure storage facilities Input numeric values (m2)Temperature Input indoor temperatures for swine

house, ambient temperatures for manure storage facilities, in °C

Treatment Record any strategies applied that may affect emissions

Information on the measurement methods

Select from traditional methods,2 OP-FTIR method,3 micrometeorologi-cal method, inverse dispersion model-ing method, SF6 (sulfur hexafluoride) tracer method,4 RPM method,5 and bLS method6

Average emission rates and standard deviation for NH3 and H2S

Input numeric values and units

1In a dry manure handling system, manure is handled as a solid, collected and stored temporarily on solid floors and removed regularly.

2Emission rate was calculated as the product of concentration and ventila-tion rate, with or without a chamber.

3The plane-integrated concentration data from open-path Fourier trans-form infrared spectrometry (OP-FTIR), along with wind speed and direction, were analyzed using an emission flux computational method.

4CH4 and SF6 concentration were measured at downwind sites, and CH4 emission rates were determined using the ratio of measured concentration and known source strength of SF6.

5Radial plume mapping method that was used for determining lagoon emission rates in National Air Emissions Monitoring Study (NAEMS) sites.

6Backward Lagrangian stochastic method that was used for determining lagoon emission rates in NAEMS sites.

Liu et al.1658

cilities. When unit conversion was not possible because of a lack of key information, the original emission data were ex-cluded from statistical analysis. A full list of included stud-ies and completed data extraction spreadsheets are available to allow for independent scrutiny of the process.

Data from the NAEMS sites were results of 2-yr continuous monitoring using consistent methods, and statistics from these studies were compiled separately to be compared with the statistics of all studies (includ-ing NAEMS). Data across studies were analyzed statis-tically using the MIXED procedures of SAS (SAS for Windows, version 9.3, SAS Inst. Inc., Cary, NC). Study (or publication) was treated as a random variable. The ra-tios of emission rate over standard deviation were used as a weighting variable. Data points with relatively small standard deviations were given more weight in the analy-sis. Effects of production stage and manure handling/storage system on emission rates were examined using Tukey’s test. Significant effects were declared at P < 0.05. Multilinear regression models were developed for certain emission sources to reflect the effects of indoor or ambi-ent air temperature, average pig weight, size of operation (number of pigs), area of manure storage, recharge inter-val of manure pits (number of days before manure pits are drained and recharged with water or lagoon effluent), etc. A backward-elimination process was used to remove the confounded terms and to reduce nonsignificant terms one by one. When a regression model failed to pass normal-ity tests, a natural log transformation was applied to the response variable (emission rate).

REsuLts ANd dIscussIoN

Statistics of NH3 and H2S Emissions from Swine Houses and Manure Storage Facilities

The ranges, means, and medians of NH3 and H2S emission rates for swine houses and manure storage

facilities are presented in Table 2. Large variations in emission rates were observed. Histograms of NH3 and H2S emission rates for swine houses and manure stor-age facilities all showed a positively skewed distribu-tion (Fig. 1 to 4). The median emission rates were more robust, and the means were all larger than the medians because of a few large values.

The median NH3 emission rate for swine houses was 2.78 kg/yr per pig, but the highest emission rate was 11 times higher. The median NH3 emission rate for swine manure storage facilities was 2.08 kg/yr per pig, and the highest emission rate was 11 times higher. The median NH3 emission rate of the NAEMS swine houses was com-parable with the median of all studies; however, the medi-an NH3 emission rate of the NAEMS manure storage fa-cilities was 5.8 times higher than the median of all studies. Results showed NH3 emission rates for manure storage facilities from the NAEMS sites were significantly higher than those from other studies when emission rates were expressed in kilograms per year per pig (P < 0.01), but the difference was not significant when emission rates were expressed in kilograms per year per square meter (P = 0.10). The discrepancy between data from the NAEMS sites and those from other studies may be related to the different methods of measurement. The NH3 emission rates of the NAEMS manure storage facilities were de-termined using the radial plume mapping (RPM) method, whereas other studies used the traditional method (emis-sion rate was calculated as the product of concentration and ventilation rate), micrometeorological method, open-path Fourier transform infrared spectrometry (oP-FtIR), or inverse dispersion modeling. Further investigation is needed to explain the discrepancy.

The median H2S emission rate for swine houses was 0.09 kg/yr per pig, but the highest emission rate was 35 times higher. The median H2S emission rate for swine manure storage facilities was 0.20 kg/yr per pig, and the highest emission rate was 7 times higher. The H2S emis-

table 2. Emission rates of NH3 and H2S from swine houses and manure storage facilities

Item

Unit1

All studies (including NAEMS) NAEMSRange2 Mean Median Range2 Mean Median

NH3Swine houses kg/yr per pig 0.33 to 31.6 (97) 3.95 ± 4.51 2.78 0.70 to 10.73 (16) 3.53 ± 2.21 2.97

kg/yr per AU 0.79 to 124.2 (101) 20.64 ± 18.09 16.43 1.75 to 24.33 (16) 15.09 ± 7.97 16.54Manure storage

facilitieskg/yr per pig 0.00 to 23.23 (74) 3.83 ± 4.43 2.08 2.66 to 23.23 (6) 11.82 ± 7.50 12.06kg/yr per m2 0.00 to 7.28 (72) 1.68 ± 1.66 1.08 0.89 to 7.28 (6) 2.90 ± 2.35 2.39

H2SSwine houses kg/yr per pig 0.00 to 3.12 (65) 0.26 ± 0.56 0.09 0.09 to 3.12 (16) 0.78 ± 1.02 0.26

kg/yr per AU 0.00 to 11.09 (70) 1.08 ± 1.07 0.55 0.28 to 6.26 (16) 2.24 ± 2.18 1.39Manure storage

facilitieskg/yr per pig 0.00 to 1.33 (27) 0.33 ± 0.37 0.20 0.05 to 1.10 (6) 0.39 ± 0.44 0.16kg/yr per m2 0.00 to 0.70 (30) 0.18 ± 0.21 0.07 0.00 to 0.34 (6) 0.12 ± 0.13 0.09

1AU = animal unit corresponding to 500 kg body mass.2Values in parentheses represent numbers of data points in each category.

Ammonia and hydrogen sulfide emissions from swine facilities 1659

sion rates from the NAEMS sites were not significantly different from those in other studies.

Emission Rates from Swine Houses: Effects of Production Stage and Manure Handling System

Means and least squares means of NH3 and H2S emis-sion rates from swine houses for various production stages and manure handling systems are presented in Table 3. Swine hoop houses had significantly higher NH3 emission rates than other manure handling systems (P < 0.01 for NH3 emission rates in both kg/yr per pig and kg/yr per AU). Effects of production stages (gestation, farrowing, nursery, or finishing) were not significant for NH3 emission rates

from swine houses (P = 0.23 and 0.15 for NH3 emission rates in kg/yr per pig and kg/yr per AU, respectively).

Deep-pit houses had higher H2S emission rates than other manure handling systems (P = 0.03 and <0.01 for H2S emission rates in kg/yr per pig and kg/yr per AU, respectively). Farrowing houses had the highest H2S emission rates, followed by gestation houses, and finish-ing houses had lowest H2S emission rates, regardless of whether emission rates were expressed in kilograms per year per pig or kilograms per year per AU (P < 0.01 in both cases). The effect of production stage on H2S emis-sion rates observed in the meta-analysis contradicted the findings of Rahman and Newman (2012), who reported that both NH3 and H2S emission rates were higher in the

Figure 1. Histogram of measured emission rates of NH3 from swine houses.

Figure 2. Histogram of measured emission rates of NH3 from swine manure storage facilities.

Liu et al.1660

gestation barns than in the farrowing barns. In their study, the gestation barns had deep-pit systems, and the farrow-ing barns had shallow pull-plug-type pits that drained manure into the corresponding gestation barn pits every 3 wk; therefore, the variation observed in H2S emission rates from barns were likely the result of different manure-handling systems as well as different production stages.

Emission Rates from Manure Storage Facilities: Effects of Production Stage and Storage Type

Means and least squares means of NH3 and H2S emission rates from manure storage facilities for vari-ous production stages and storage types are presented in Table 4. No storage type or production stage effects were observed for NH3 emission rates (in kg/yr per pig, P = 0.45 and 0.24, respectively; or kg/yr per m2, P = 0.75

and 0.30, respectively) or H2S emission rates (in kg/yr per pig, P = 0.47 and 0.13, respectively; or kg/yr per m2, P = 0.06 and 0.60, respectively). Harper et al. (2006) reported that NH3 emission rates on an animal basis in-creased as pigs aged, with nursery animals having the lowest rates and sows having the highest, agreeing with the results of this meta-analysis.

Regression Models for NH3 and H2S Emission Rates

Regression models for NH3 and H2S emission rates were developed for finishing houses with deep pits, recharge pits, and lagoons (Table 5) to reflect the effects of indoor or ambient air temperature, average pig weight, size of opera-tion (number of pigs), area of manure storage, recharging interval of manure pits, etc. The indoor air temperatures ranged from 8°C to 28°C, average pig weights ranged from

Figure 3. Histogram of measured emission rates of H2S from swine houses.

Figure 4. Histogram of measured emission rates of H2S from swine manure storage facilities.

Ammonia and hydrogen sulfide emissions from swine facilities 1661

table 3. Means and least squares means of NH3 and H2S emission rates from swine houses by various production stages and manure handling systems1

Swine house type Gestation Farrowing Finishing Nursery Least squares meanNH3 emission rates, kg/yr per pig

Hoop (0) (0) 12.93 ± 0.89 (2) (0) 14.80 ± 1.97b (2)Dry (0) (0) 4.19 ± 4.77 (7) (0) 3.26 ± 1.22a (7)Deep pit 5.85 ± 5.13 (3) 7.030 (1) 3.57 ± 2.00 (36) 0.66 (1) 4.30 ± 0.90a (41)Recharge pit 14.61 ± 14.39 (4) 7.80 ± 10.97 (3) 2.38 ± 1.48 (32) 0.860 (1) 2.90 ± 0.80a (40)Drain pit 3.44 ± 0.09 (2) 2.18 ± 2.09 (2) 1.32 ± 0.40 (3) (0) 3.13 ± 0.84a (7)Least squares mean 6.69 ± 1.06 (9) 5.46 ± 1.74 (6) 4.89 ± 0.49 (80) (2)

NH3 emission rates, kg/yr per AUHoop (0) (0) 69.18 ± 8.22 (2) (0) 73.62 ± 13.69b (2)Dry 8.67 ± 1.94 (2) (0) 32.38 ± 40.70 (7) (0) 8.05 ± 9.13a (9)Deep pit 10.59 ± 6.54 (7) 17.18 (1) 24.67 ± 13.52 (34) 16.04 (1) 16.03 ± 5.60a (43)Recharge pit 7.39 ± 1.23 (2) 4.08 ± 4.66 (2) 17.95 ± 13.26 (32) (0) 8.77 ± 4.99a (36)Drain pit 8.61 ± 0.23 (2) 2.51 ± 2.63 (6) 7.81 ± 2.02 (3) (0) 10.83 ± 4.96a (11)Least squares mean 20.53 ± 6.88 (13) 16.90 ± 9.13 (9) 32.95 ± 3.83 (78) (1)

H2S emission rates, kg/yr per pigHoop (0) (0) 0.015 ± 0.004 (2) (0) 1.457 ± 0.378a,b (2)Dry (0) (0) 0.017 ± 0.007 (6) (0) 1.224 ± 0.309a,b (6)Deep pit 1.709 ± 1.503 (3) 1.065 (1) 0.136 ± 0.127 (25) 0.455(1) 1.545 ± 0.205b (30)Recharge pit 0.110 ± 0.014 (2) 2.790 (1) 0.071 ± 0.057 (17) (0) 0.970 ± 0.183a,b (20)Drain pit 0.275 ± 0.007 (2) 1.375 ± 0.007 (2) 0.023 ± 0.006 (3) (0) 0.778 ± 0.190a (7)Least squares mean 1.098 ± 0.245b (7) 2.499 ± 0.309c (4) -0.012 ± 0.121a (53) (1)

H2S emission rates, kg/yr per AUHoop (0) (0) 0.078 ± 0.004 (2) (0) 3.690 ± 1.173a,b (2)Dry 0.730 (1) (0) 0.121 ± 0.048(6) (0) 2.132 ± 1.186a,b (6)Deep pit 2.309 ± 2.063 (7) 2.604 (1) 1.019 ± 0.912 (24) 11.089 (1) 4.068 ± 0.686b (33)Recharge pit 0.304 ± 0.039 (2) 7.707 (1) 0.525 ± 0.391 (17) (0) 1.450 ± 0.620a (20)Drain pit 0.688 ± 0.675 (2) 1.703 ± 1.737 (4) 0.137 ± 0.038 (3) (0) 0.754 ± 0.601a (9)Least squares mean 1.791 ± 0.822a (12) 5.056 ± 0.960b (6) 0.410 ± 0.460a (52) (1)

a–cValues within the same effect section without a common letter differ significantly (P < 0.05).1Values in parentheses represent the number of data points in each category. AU = animal unit corresponding to 500 kg body mass.

table 4. Means and least squares means of NH3 and H2S emission rates from swine manure storage facilities by vari-ous production stages and storage systems1

Storage system Gestation Farrowing Finishing Nursery Least squares meanNH3 emission rates, kg/yr per pigLagoon (0) 8.92 ± 6.68 (10) 3.70 ± 3.74 (47) 0.020 (1) 5.35 ± 1.53 (58)Slurry tank (0) (0) 1.85 ± 2.28 (12) 0.45 ± 0.38 (4) 3.01 ± 2.96 (16)Least squares mean (0) 6.00 ± 3.79 (10) 4.36 ± 1.51 (59) 2.19 ± 1.89 (5)NH3 emission rates, kg/yr per m2

Lagoon (0) 2.26 ± 1.69 (11) 1.59 ± 1.81 (45) 0.030 (1) 3.02 ± 0.68 (57)Slurry tank (0) (0) 1.67 ± 1.15 (11) 1.35 ± 1.30 (4) 3.50 ± 1.49 (15)Least squares mean (0) 4.27 ± 1.71 (11) 2.47 ± 0.76 (56) 3.04 ± 0.88 (5)H2S emission rates, kg/yr per pigLagoon (0) 0.387 ± 0.321 (8) 0.256 ± 0.344 (13) (0) 0.388 ± 0.155 (21)Slurry tank (0) (0) 0.438 ± 0.554 (5) 0.204 (1) 0.554 ± 0.181 (6)Least squares mean (0) 0.516 ± 0.278 (8) 0.774 ± 0.109 (18) 0.121 ± 0.271 (1)H2S emission rates, kg/yr per m2

Lagoon (0) 0.128 ± 0.117 (10) 0.121 ± 0.160 (14) (0) 0.360 ± 0.063 (24)Slurry tank (0) (0) 0.378 ± 0.300 (5) 0.656 (1) 0.660 ± 0.071 (6)Least squares mean (0) 0.374 ± 0.115 (10) 0.450 ± 0.042 (19) 0.556 ± 0.114 (1)

1Values in parentheses represent numbers of data points in each category.

Liu et al.1662

21 to 249 kg, the number of pigs ranged from 6 to 13,680, the recharge interval of manure pits ranged from 1 to 42 d, ambient air temperatures ranged from 2°C to 32°C, and areas of lagoons ranged from 1,131 to 97,600 m2.

For finishing houses with deep pits or recharge pits, NH3 emission rates were positively related to indoor air temperature. Finishing operation lagoons had NH3 emis-sion rates that were positively related to ambient air tem-perature (P < 0.01). Effects of temperature on H2S emis-sion rates were not significant. Many individual studies observed the effects of temperature on NH3 emission rates (Harper et al., 2000, 2004; Heber et al., 2000; Aneja et al., 2000, 2008; Pelletier et al., 2006; Blunden and Aneja, 2008), and so did the results of the meta-analysis. Aneja et al. (2000, 2008) and Pelletier et al. (2006) both reported NH3 emission rates increased exponentially with increasing lagoon or manure temperature.

The recharge interval of manure pits in finishing hous-es significantly affected H2S but not NH3 emission rates. Swine houses with pits that had longer recharge intervals emitted more H2S (P < 0.01), a finding that is in agree-ment with the findings of Predicala et al. (2007) and Lim et al. (2004). Predicala et al. (2007) reported that daily re-moval of manure resulted in significantly lower H2S emis-sions but found no difference for NH3 emissions. Lim et al. (2004) observed that H2S emissions significantly increased as recharge intervals increased from 7 to14 d and to 42 d, but the effect on NH3 emissions was not significant.

The NH3 and H2S emission rates from swine hous-es in kilograms per year per pig increased with increas-ing pig weights. When expressed in kilograms per year per AU, NH3 emission rates were no longer influenced by pig weight, but for finishing houses with recharge pits, H2S emission rates in kilograms per year per AU remained positively related to pig weight (P = 0.01). The H2S emission rates were also influenced by size of operation. Deep-pit finishing houses with larger pig numbers tend to have higher H2S emission rates in ki-lograms per year per AU (P = 0.02).

Sizes of Swine Farm That May Trigger the Need to Report NH3 or H2S Emissions

The EPCRA and CERCLA require reporting of NH3 and H2S emissions that exceed 45.4 kg/d. Swine farm sizes that may approach the limit to report NH3 and H2S emissions under EPCRA and CERCLA were calculated and are presented in Table 6. The median emission rate of NH3 from swine facilities was 17 times higher than that of H2S; therefore, swine farm sizes that may reach the 45.4 kg/d threshold were much smaller for NH3 than for H2S. The farm size that may approach the limit to report NH3 emissions is 3,410 pigs on the basis of the median NH3 emission rate (4.86 kg/yr per pig), but it can be as low as 992 pigs on the basis of the 90th percentile emis-sion rate (16.71 kg·yr-1·hd-1).

NH3 Concentrations in the Vicinity of Swine Facilities

The Agency for Toxic Substances and Disease Registry (AtsdR) has suggested minimum risk levels (MRL) for NH3 and H2S to protect sensitive populations (ATSDR, 2008). The MRL for NH3 are 1,700 and 1200 and 70 µg/m3 (1,700 and 100 ppb) for an acute (1 to 14 d

table 5. Regression models for NH3 and H2S emission rates from various emission sourcesEmission sources Regression model1

Finishing houses with deep pits NH3 emission rates in kg/yr per pig = EXP (-0.63 + 0.019W + 0.025Ti)NH3 emission rates in kg/yr per AU = EXP (2.69 + 0.026Ti)H2S emission rates in kg/yr per pig = EXP (-3.45 + 0.0024W + 0.00038N)H2S emission rates in kg/yr per AU = EXP (-1.10 + 0.000061N)

Finishing houses with recharge pits NH3 emission rates in kg/yr per pig = EXP (-1.42 + 0.013W + 0.056Ti)NH3 emission rates in kg/yr per AU = EXP (1.55 + 0.055Ti)H2S emission rates in kg/yr per pig = EXP (–5.93 + 0.038W + 0.047R)H2S emission rates in kg/yr per AU = EXP (-2.83 + 0.022W + 0.049R)

Lagoons for finishing operations NH3 emission rates in kg/yr per pig = EXP (-0.38 + 0.070Ta)NH3 emission rates in kg/yr per m2 = EXP (-1.38 + 0.074Ta)

1AU = animal unit corresponding to 500 kg body mass; Ti = indoor air temperature in swine houses, °C; Ta = ambient air temperature, °C; W = average weight of pigs, kg; N = number of pigs in the farm; R = recharge interval of manure pits, d.

table 6. Size of swine farm that may trigger the need to report NH3 or H2S emissions

Basis

Emission rate (kg/yr per pig) Size that may reach the 45.4 kg/d NH3 or H2S

per day thresholdSwine house

Manure storage

Total

Median emission ratesNH3 2.78 2.08 4.86 3,410 pigsH2S 0.09 0.20 0.29 57,141 pigs

75th percentile emission ratesNH3 4.49 6.27 10.76 1,540 pigsH2S 0.20 0.63 0.83 19,965 pigs

90th percentile emission ratesNH3 7.17 9.54 16.71 992 pigsH2S 0.47 0.83 1.30 12,747 pigs

Ammonia and hydrogen sulfide emissions from swine facilities 1663

continuous) and chronic (>365 d continuous) exposure, respectively. In the following analysis, we compared the average values of observed concentrations with the MRL, although the concentrations were not necessar-ily continuous measurements for the MRL period. The average NH3 concentration at the edge of the emission sources (swine houses or lagoons) was 3.8 ± 3.6 mg/m3 (ranging from 0.2 to 11 mg/m3), which is higher than the acute MRL for NH3 (1200 µg/m3). The ambient NH3 concentrations in the vicinity of swine facilities de-creased quickly to less than the chronic MRL (70 µg/m3) as distances from emission source increased (Fig. 5). At distances of 30 to 1,185 m from emission sources, the average ambient NH3 concentration was 46 ± 46 µg/m3 (ranging from 7 to 190 µg/m3). In comparison, the av-erage background ambient NH3 concentration outside swine production areas was 5.4 ± 2.4 µg/m3, whereas Godbout et al. (2009) and Donham et al. (2006) report-ed the average ambient NH3 concentration within swine production areas was 8.2 ± 3.8 µg/m3. The average am-bient NH3 concentration in the vicinity of swine facili-ties (46 ± 46 µg/m3 at distances from 30 to 1,185 m) was about 8 times higher than the average background ambient NH3 concentration in areas not influenced by swine production facilities (5.4 ± 2.4 µg/m3).

H2S Concentrations in the Vicinity of Swine Facilities

The MRL for H2S are 97 and 28 µg/m3 (70 and 20 ppb) for acute and intermediate (15 to 365 d continuous) expo-sures, respectively. The average H2S concentration at the edge of the emission sources (swine houses or lagoons)

was 56 ± 66 µg/m3 (ranging from 3 to 203 µg/m3), which is less than the acute MRL (97 µg/m3) but higher than the intermediate MRL (28 µg/m3) for H2S. The ambient H2S concentrations in the vicinity of swine facilities decreased quickly to less than 20 ppb as distances from emission source increased (Fig. 6). The average ambient H2S con-centration was 4.3 ± 8.6 µg/m3 at distances of 30 to 1,185 m from emission sources. In comparison, Godbout et al. (2009) and Donham et al. (2006) reported average ambient H2S concentrations of 2.6 ± 1.5 µg/m3 in areas not influ-enced by swine production facilities.

Conclusions

On the basis of meta-analysis of published emission data, the following conclusions can be made.

1) Many factors can affect NH3 and H2S emission rates from swine, and large variations were ob-served in the literature. The emission rates of NH3 were much higher than those of H2S. The farm size that may trigger the need to report NH3 emissions under EPCRA is 3,410 pigs on the basis of the me-dian NH3 emission rates, but it can be as low as 992 pigs on the basis of 90th percentile emission rates.

2) The NH3 emission rates for manure storage facili-ties from NAEMS sites were significantly higher than those from other studies when emission rates were expressed in kilograms per year per pig. The discrepancy may be related to the different sam-pling and computing methods, and further investi-gation is needed.

Figure 5. Measured NH3 concentrations at various distances from swine facilities.

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3) Swine hoop houses had significantly higher NH3 emission rates than other manure-handling systems, whereas deep-pit houses had the highest H2S emis-sion rates.

4) Farrowing houses had the highest H2S emission rates, followed by gestation houses, and finishing houses had the lowest H2S emission rates. The ef-fects of production stages were not significant for NH3 emission rates from swine houses.

5) No significant effects of production stage or stor-age type were observed for NH3 and H2S emission rates from manure storage facilities.

6) The NH3 emission rates increased with increasing air temperature, whereas the effects of air tempera-ture on H2S emission rates were not significant.

7) The recharge interval of manure pits significantly affected H2S but not NH3 emission rates. The H2S emission rates were also influenced by the size of the operation. Farms with longer recharge intervals or larger pig numbers tended to have higher H2S emission rates.

8) Although NH3 and H2S concentrations at the edge of swine houses or lagoons were often higher than corresponding acute or intermediate MRL, they decreased quickly to be than corresponding chron-ic or intermediate MRL as distances from emission source increased. At distances 30 to 1,185 m from emission sources, the average ambient concentra-tions for NH3 and H2S were 46 ± 46 µg/m3 and 4.3±8.6 µg/m3, respectively.

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