Odor and Air Emissions From Poultry Facilities

In Arkansas, production agriculture is a $4 billion annual industry, three-fourths of which comes from livestock, mainly poultry (EPA, 1998). Modern production agriculture is increasingly regarded as a major source of air pollutants. The trend toward larger and more concentrated animal production coupled with the general public's increasing intolerance of odors mandates the control of odors, gases, and dust.

Animal feeding operations (AFOs) have become increasingly consolidated, specialized, and regionally concentrated in the last decade (Sweeten et al., 2004). Air quality concerns are becoming a major environmental issue. Primary sources of odors, gases, and dust from  production agriculture units include:

Management practices are an important factor in determining emissions from animal feeding operations; perhaps of equal or greater importance than the specie itself (Powers and Bastyr, 2004). Many of the foul-smelling compounds emitted from animal production operations are as a result of decomposition of livestock and poultry wastes in the absence of air (anaerobic decomposition). Aerobic decomposition (decomposition in the presence of air) generally produces fewer odorous by-products than anaerobic decay, but aerobic decay can enhance volatilization of gaseous compounds that produce some odors and degrade environmental quality (Powers, 2003). While little information is available on the environmental impact of odor and airborne contaminates, as many as 100 compounds have been identified in air samples collected from animal production facilities (Miner, 1995). However, it is estimated that one third of the methane produced each year comes from industrial sources, one third from natural sources and one third from agriculture, primarily animals and manure storage units (Powers, 2003).

Odor from animal feeding operations is not caused by a single compound, but is rather the result of a large number of contributing compounds including NH3, volatile organic compounds (VOCs), and H2S (National Academy of Sciences, 2003). A further complication is that odor involves a subjective human response. What is objectionable to some is not to everyone. The most common odor complaint by the public associated with poultry production is related to land application of manure. When manure is land applied, it is typically applied to an area up to 700 times the surface area of the original storage, creating a large but short-term downwind odor plume (Heber and Jones, No Date). For odor to be detected, odor-producing compounds must have been produced, released and transported downwind. A complex mixture of gases produce the odor associated with a poultry operation. Some of the principal classes of odorous compounds are: amines, sulfides, volatile fatty acids, indoles, skatoles, phenols, mercaptans, alcohols, and carbonyls (Powers, 2003). Ammonia creates strong odors near manure storage areas and poultry buildings themselves, but is not a significant component of odor downwind from a poultry farm. Ammonia is highly volatile and moves upward in the atmosphere quickly when released.

Dust, while a problem in its own right, can also carry gases and odors. Dust is generated from feed, manure, and the birds themselves. A large portion of odor associated with exhaust air from mechanically ventilated poultry houses is dust particles that have absorbed odors from within the houses. Factors determining the amount of dust include cleanliness of the houses, bird activity, temperature, relative humidity, ventilation rate, and stocking density.

The issue that most often brings air emissions to the attention of public officials is the frequency of complaints about strong and objectionable odors voiced by neighbors of large animal feeding operations. Equally important are the various substances in air emissions that contribute to environmental degradation (National Academy of Sciences, 2003). Concern is understandable since between 1982 and 1997, the number of animal feeding operations in the United States decreased by 51%, while livestock production increased 10% (Gollehon et al., 2001). This indicates that there are fewer farms with more animals on those farms than in the past; and hence, more animal waste in a smaller area.

Currently, there is no comprehensive, sound, science-based set of data on emissions from AFOs. An understanding of AFO air emissions and their effects will require the expertise of numerous scientific disciplines, including animal nutrition and physiology, farm practices, atmospheric chemistry, meteorology, air monitoring, statistics, epidemiology and toxicology, agricultural engineering, economics, and other related disciplines. Emission rates can vary with changes in the management of the animals, their feed or weather conditions and may vary tenfold or more during periods as short as an hour or long as a year. This variability in AFO air emission rates is perhaps the most serious impediment to generating a sound, reliable database (National Academy of Sciences, 2003).

The EPA has a variety of needs for more accurate estimates of air emissions from AFOs, including the following:

As mentioned earlier, land application of manure generates the most consistent and noisy odor complaints. Land application offers acres and acres of volatile compound generation versus the relatively contained sources of air emissions from manure storage and livestock housing. Thus, keeping poultry manure in the house or in dry storage is the first line of defense against odor and gas emission complaints (Wheeler, 2002). Also consider topography and air drainage patterns when considering constructing new or purchasing existing facilities in hilly areas. In such areas, during the evening hours there are often periods of little or no wind. In these still periods air near the ground will begin to cool and, because cool air is heavier than warm air, it drifts down slope. Poultry houses scattered across hills are in the path of this air moving down slope and any odors generated by these facilities may be picked up and carried down wind to towns or communities located in the valleys below.

A wide variety of manure management technologies and strategies have been considered over the last 30 years (ASAE, 1971). The systems currently in place are those that proved the most cost-effective and reliable at achieving their objectives. For the most part, those objectives have not included minimization of emissions, but have centered on water quality protection, nuisance avoidance, animal environment protection, and worker health protection. (National Academy of Sciences, 2003).

Even though there is no comprehensive, science-based set of data on emissions from AFOs, almost all producers realize that the lack of data has not stopped complaints or legal actions against production units. Thus, producers must continue to deal with the situation.

Shelterbelts of trees or shrubs have been used extensively in some parts of the country for snow and wind protection. Shelterbelts around poultry operations can offer improved aesthetics of production facilities and may help reduce any environmental impact (actual or perceived) of the operation since many people tend to "smell" with their eyes. Shelterbelts may also offer odor reduction by creating turbulence that encourages the mixing of odorous air with fresh air, promoting the settling of dust where wind speeds are lower, physical interception of dust and particulates or adsorption and absorption of odor compounds on the foliage of trees or shrubs (Wheeler, 2002).

One of the best ways to lessen complaints about any animal production facility is to run a clean, neat, tidy operation. Make it a point to know who your neighbors are and develop a good relationship with them. Personally tell your neighbors what your plans are so that they do not hear information secondhand that may or may not be accurate. Stay or become involved with community activities and attend public meetings related to area farming practices. Make the general population aware that you are concerned about the environment and are open to new ideas. Always check with neighbors before spreading manure to make sure you do not disrupt someone's family reunion or weekend events. Farming is a business and all businesses need customers. Most likely your neighbors go to the store and purchase the same product you produce. Therefore, it is important to keep your neighbors/customers happy.

An effective strategy to reduce gas, odor and dust emissions from livestock and poultry operations will likely be site specific since no one practice will work at every operation. Plan on using a variety of strategies with the goal being to reduce the overall generation of emissions from your operation. To some producers it may not seem like that big of a problem just yet; however, as rural and urban populations increasingly share more and more land with one another, odor and air emissions from livestock facilities has the potential to make the issue of land application of animal wastes pale in comparison. Recall all that has happened with land application rules and guidelines over the past 5-10 years. Ten years ago land application of wastes did not seem like a big problem. Now consider what could happen with air emission standards. The time for modern production agriculture to address the issue has come.