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Air Issues Associated with Animal Agriculture: A North American Perspective

by 5m Editor
8 June 2011, at 12:00am

Academic experts have examined a large amount of data and provide analysis on a wide scope of issues, from greenhouse gas (GHG) emissions to the logistics of manure storage facilities, in this report for the US Council for Agricultural Science and Technology (CAST). Here, we cover the report abstract and the section on swine production.


The purpose of this CAST Issue Paper is to go beyond the generalisations and accusations often associated with the air quality topic. Experts from six universities examine a large amount of data and focus their information and conclusions around the key livestock areas: swine, poultry, dairy and beef. Their critical analyses look at a wide scope of issues, from greenhouse gas (GHG) emissions to the logistics of manure storage facilities. The US Environmental Protection Agency (EPA) is increasing efforts to monitor emissions from agriculture, so further research is important for all parties involved, and this paper provides solid, science-based information.

Studies indicate that large livestock production facilities lower the value of residences within 4.8 kilometres (km; three miles) of the facility. Other economic studies also indicate, however, that the businesses increase economic activity in the county and state. For the greater good of the rural community, a compromise needs to be reached between the positive and negative impacts of livestock production facilities using a common-sense approach that considers both regulatory and market forces.

Air emissions attributed to animal agriculture consist of odorous and gaseous compounds as well as particulate matter associated with manure and animal management. While localised problems associated with odour tend to get highlighted, gaseous compounds having localised or regional impacts, such as ammonia, and global concerns, such as those attributed to GHG, are becoming huge regulatory issues.

This paper looks at some of the mitigation techniques being employed to decrease the effects of the aerial pollutants. The authors also examine the disparity between the results of the EPA’s estimations of GHG emissions and the findings of the Food and Agriculture Organization (FAO) of the United Nations.

A few of the many specific findings include: diet composition has a significant impact on emissions; mitigation methods, such as covering the manure storage surface, can greatly decrease odor emissions; and aeration of the storage basin or employing anaerobic digestion of the manure will also reduce the odour, but with higher costs. The much-quoted study entitled Livestock’s Long Shadow distinguishes between intensive and extensive livestock production; US production is intensive so it does not have the GHG emissions associated with poor feed quality and deforestation.

Pig Production

In pork production, gaseous compounds are primarily generated from anaerobic microbial decomposition of organic matter in animal manure and spoiled feedstuff. Gaseous compounds originate from the breakdown of various specific components of the pig’s diet or normal excretion of compounds from metabolism; therefore, diet composition has a significant impact on the concentrations and emissions of gaseous compounds. Greenhouse gases (methane, CH4; nitrous oxide, N2O; and carbon dioxide, carbon dioxide) are derived primarily from microbial decomposition of manure in addition to normal animal respiration (CO2). Particulate matter generates from feed systems, dried manure and animal dander. Airborne microbes, otherwise classified as 'bioaerosols', generate from animals and manure and may be attached to particulate matter (PM). Bioaerosols need not be alive and viable to impair human health, as in the case of bacterial endotoxin.

Sources of gaseous emissions in pork production include the buildings that house the animals, manure storage structures and manure during and after land application. Most swine are housed in either mechanically or naturally ventilated enclosed buildings. Manure is typically stored in liquid form within these buildings in a pit beneath the animal space for a period of only several days to as long as a year. Deep pits (8–10 feet deep) are commonly used to facilitate long-term storage of manure within these buildings, but long-term storage allows manure to decompose and release resulting biogases. In another common system, often referred to as a pull-plug system, manure is stored for only about a week within shallow pits and then removed from the buildings routinely to outside storage facilities to keep gas levels low within the animal building. If not covered, these outside storage facilities (earthen, above- or in-ground concrete or steel tanks) can emit considerable amounts of gas. Swine also may be housed in buildings (such as hoop barns) that use added bedding – typically straw, cornstalks or sawdust – and produce solid manure. Swine manure is almost always applied to crop land as fertiliser.

Following is a discussion of both the concentrations of air pollutants inside or near swine buildings and manure storages and the mass flow or emissions of the airborne pollutants from pork production sites, in order of their perceived importance.


Ammonia concentrations inside studied swine confinement buildings have been shown to vary widely, from as low as 1.9 parts per million (ppm) to as high as 25.9 ppm, depending on the cleanliness condition of the building (Duchaine, Grimard, and Cormier 2000) and on the time of year and/or barn ventilation rate (Heber et al. 1997, 2000, 2004, 2005). Generally, farrowing rooms and nurseries had lower NH3 concentrations than swine gestation or grow-finishing facilities (Jacobson et al. 2006; Zhu et al. 2000). As one might expect, ambient ammonia concentrations diminished rapidly with the downwind distances from swine buildings (Stowell et al. 2000).

Arogo, Westerman and Heber (2003) conducted a literature review on research studies that reported ammonia emissions from swine operations including buildings, lagoons and field applications of swine wastes. They concluded that there are many factors affecting ammonia emission rates including housing type; animal size, age, and type; manure management, storage, and treatment; and climatic variables. Because of these many factors, it is difficult to determine specific ammonia emission values for all types of swine operations across the country. In a multi-state research project involving different life-cycle aspects of pork production (Jacobson et al. 2004, 2006), average ammonia emissions were 48 and 30g/day/animal unit (g/day/AU) for gestating and farrowing sows, respectively, and average ammonia emissions for the finishing barns ranged from 102 to 130g/day/AU in a deep-pit system and 77 to 81g/day/AU from a pull-plug barn. An observation by Heber and colleagues (2005) was that hourly ammonia emission was positively correlated with indoor and outdoor temperatures, ventilation rate and total live pig weight. Pig activity and ammonia emission rate displayed similar diurnal patterns.

Carter, Lachmann and Bundy (2008) showed that changing the diet of pigs can have a major impact on ammonia emissions from swine production buildings. They reported that the use of a low-protein and synthetic amino acid diet compared to a control diet decreased ammonia emissions by almost half.


Because gaseous compounds associated with odour vary widely in molecular weight and odorant strength, the concept of an “odour unit” (OU) was developed as a means of normalising the specifically odour-related effect of an arbitrarily selected odorant or mixture of odorants. In general, an OU is defined as the mass of a reference odorant (e.g., n-butanol) that, when dispersed in the gas phase into odour-free air, results in an odour precisely at the human detection threshold for that reference odorant. This definition allows scientists to evaluate the strength of an arbitrary mixture of odorants using dilution olfactometry and translate the mixture’s ‘dilutions to threshold’ value into the pseudo-mass quantity OU. Refer to Table 1 for swine building odour emission and concentration studies.

Table 1. Odour emissions/concentrations levels in sample studies
Source Odour emissions Odour concentrations Reference
1,200-head grow-finish pig buildings 10,000–12,000 OU/sa 650–1,600 OU/m3 b Jacobson, Hetchler and Schmidt (2007)
Fan-ventilated swine finishing buildings flushed daily with lagoon effluent Mean of 23.5 OU/s/AU Mean of 519 OU/m3 Heber et al. (2004)
Swine nursery buildings with under-floor liquid manure storage pits 51 OU/s/pig–2.1 OU/s/m2 190 OU/m3 in exhaust air; 18 OU/m3 outside building Lim, Heber and Ni (1999)
Four 1,000-head finishing buildings Average of 96 OU/s/pig or 5.0 OU/s/m2 Average of 294 OU/m3 (ranged from 12 to 1,586 OU/m3) Heber et al. (1998)
a Per second
b Per cubic metre

Volatile Fatty Acids and Volatile Organic Compounds

Volatile organic compounds measured at three swine farms (8,000-head nursery; 2,000- and 3,000-head finishing buildings) showed mean total VOC emissions of 204, 291 and 258μg/s/m2 (micrograms/second/square metre) for the nursery and two finishing buildings, respectively (Bicudo et al. 2002). A wean-to-finish pig growth study conducted by Radcliffe and colleagues (2008) reported volatile fatty acid (VFA) emissions with a range of 30 to 70 and 40 to 100 millimoles/day/pig from pigs fed a low-nutrient excretion diet and a control commercial diet, respectively.

Hydrogen Sulphide

Indoor mean hydrogen sulphide (H2S) concentrations have been found to be higher in gestating buildings (600 parts per billion [ppb]) than in farrowing barns (300ppb), according to a study by Jacobson and colleagues (2006) involving different phases of pork production facilities. Hydrogen sulfide concentration levels spiked briefly to 3,000ppb or 3ppm in the barn when liquid manure was drained (pull-plug system) in the gestation sow building. Swine finishing buildings that are mechanically ventilated with deep-pit manure storage had mean indoor concentrations of hydrogen sulphide from 38 to 536 ppb over a period of six months (Ni et al. 2002a,b).

Farrowing (lactating sow) barns give off less hydrogen sulphide emissions than gestating sow buildings, as do finishing pigs in pull-plug versus deep-pit barns (Jacobson et al. 2006). Hydrogen sulphide emissions from a 1,200-head grow-finish pig building studied by Jacobson, Hetchler and Schmidt (2007) ranged from 400 to 775g/d (0.3 to 0.65g/d/pig) over three seasons (winter, spring and summer). Also, mean hydrogen sulphide emissions for two 1,000-head finishing buildings were 590g/d/building or 6.3g/d/AU (Ni et al. 2002c). The average hydrogen sulphide emission for the entire study was 0.72g/d/pig. These rates were directly proportional to room temperatures and air flow rates. Pig size was not a significant parameter.

Greenhouse Gases

Greenhouse gas emissions specifically related to swine production systems in Canada were estimated by Laguë (2003) as a total of 1,835 kilotons (kt) carbon dioxide. This corresponds to approximately three per cent of the total Canadian GHG agricultural emissions, 0.3 per cent of the total Canadian anthropogenic GHG emissions, or 0.006 per cent of the total world GHG emissions. A majority of carbon dioxide generation in pig operations is due to carbon dioxide expiration from animals. The amount of carbon dioxide released from the manure in a pig production building (partially slatted floor and shallow pits), as determined by Ni and colleagues (1999), represents 37.5 per cent of the quantity of carbon dioxide exhaled by the animals, whereas Lim and colleagues (1998) reported carbon dioxide emissions from an 880-head grow-finish swine building with total slotted floors and tunnel ventilation as 3.0 kilograms/day/pig (kg/d/pig), ranging from 1.2 to 9.5.

Methane and nitrous oxide (N2O) emissions varied from 48 to 54g/d/AU and from 0.8 to 2.1 g/d/AU, respectively, for a slatted-floor pig finishing barn studied by Osada, Ram, and Dahl (1998). Methane emissions of 160g/d/AU were measured from deep-pit and pull-plug pig finishing facilities (Zahn et al. 2001), while nitrous oxideO emissions from the liquid manure management system of swine production in North America were estimated to be 20g/yr/animal (Laguë 2003).

Particulate Matter

Particulate matter (PM10 – PM with aerodynamic diameter of less than or equal to 10 micrometres [µm]) emission from a 1,200-head grow-finish pig building studied by Jacobson, Hetchler and Schmidt (2007) ranged from 180 to 900g/d (0.15 to 0.75g/d/pig) and the PM10 concentrations varied from 200 to 650µg/m3 over three seasons (winter, spring and summer). Total suspended particulates (TSP) and PM10 from fan-ventilated swine finishing buildings that were flushed daily with lagoon effluent showed a mean PM10 emission of 1.6g/d/AU and a mean PM10 concentration of 334µg/m3 (Heber et al. 2004). Total suspended particulate concentrations measured by Duchaine, Grimard and Cormier (2000) in eight swine confinement buildings with a range of cleanliness conditions resulted in a mean value of 3.54mg/m3 (3.54 milligrams/m3; ranging from 2.15 to 5.60mg/m3). Concentrations of TSP in swine farrowing buildings were significantly lower than mean TSP concentrations in pig finishing buildings (Cormier et al. 1990).


Microbial concentrations in eight swine confinement buildings with a range of cleanliness conditions were determined by Duchaine, Grimard and Cormier (2000). The average concentrations were: moulds, 883 colony-forming units per cubic metre (cfu/m3); total bacteria, 4.25 × 105 cfu/m3; and endotoxin, 4.9 × 103 endotoxin units/m3. Airborne microorganisms isolated by Cormier and colleagues (1990) in two swine farrowing and two pig finishing buildings showed total bacteria concentrations averaging 1.51 × 105 cfu/m3 and 1.83 × 105 cfu/m3 for each of the farrowing units and 4.92 × 105 cfu/m3 and 5.44 × 105 cfu/m3 for each of the two finishing barns. Bioaerosols assayed in 24 swine confinement buildings showed mean concentrations of bacteria and fungi ranging from 7.32 to 9.64 × 104 cfu/m3 and 1.97 to 5.85 × 103 cfu/m3, respectively. Other mean total bacterial concentrations were 5.9 × 105 cfu/m3 (Haglind and Rylander 1987) and 1.08 × 105 cfu/m3 (Heederick et al. 1991) for swine confinement buildings.

Further Reading

- You can view the full report, including the reference list, by clicking here.

June 2011