Ammonia (NH₃) from agricultural activities has become a public concern as it impacts health, can cause acidity of the natural environment, algae to grow in lakes, and formation of small particles in the air (NRC, 2003). It is a colorless gas and has a sharp, pungent odor that people can smell at about 5 to 18 ppm (parts per million). Ammonia has a familiar smell because many household and industrial cleaners and window-cleaning products contain ammonia. It is lighter than air and highly soluble in water. In water it becomes positively charged and is called ammonium ion (NH₄+). The ammonium turns into gaseous ammonia when the liquid is exposed to open air.
Ammonia occurs naturally and is produced by human activity. It is naturally generated by microorganisms when they decompose organic matter or by man-made synthetic processes used for the production of fertilizers, nitric acids, fuels, explosives, and refrigerants. Liquid ammonia as a fertilizer can be applied directly into soil on farm fields. It is also used to make fertilizers for farm crops, lawns and plants.
Ammonia emission from animal feeding operations
All animals consume protein and other forms of nitrogen (N) in feed to produce N rich meat, milk or eggs. Unfortunately, the conversion of feed to animal product is often inefficient, with 50–80% of the nitrogen in the feed being excreted in animal waste. As microbes begin decomposing the waste, ammonia is released, making manure and urine a primary source of ammonia (NH₃). Therefore, major sources of NH₃ emissions from animal feeding operations are animal buildings, manure storages, and land application of manure (Figure 1).
Agricultural activities, livestock and poultry farming in particular, are the largest contributors to ammonia (NH₃) emissions according to the USEPA national emission inventory (USEPA, 2004). Among the livestock and poultry industry sectors, dairy and beef cattle production contributes about 54% of total ammonia emissions to the atmosphere, poultry production 33%, and swine 12% (Figure 2).
How is ammonia emission generated?
Ammonia (NH₃) is generated because of nitrogen in the feces and urine of pigs and cattle and the uric acid of poultry manure. Ammonia forms from the biological and chemical breakdown of manure protein, uric acid, and urea during manure storage and decomposition. When ammonia is produced with water present, it becomes ammonium and stays in the liquid under specific conditions of pH. At low pH (<7, acidic conditions), 99% of the ammonia remains in the liquid as ammonium (NH₄+). However, at high pH (>7, basic conditions) some of the ammonium converts to NH₃, the gas forms and escapes. When the pH = 9.25, 50% is ammonia gas and 50% liquid ammonium (NH₄+).
Ammonia formation and emission is greatly affected by manure moisture content, temperature, nitrogen content, aeration conditions, manure pH value, and chemical and microbiological activities. Research, considering these factors, has shown ammonia emissions can be reduced through:
- separation of urine and feces,
- separation of manure from oxygen,
- keeping low temperature,
- low protein feed,
- manipulation of manure pH value.
Ammonia gas diffuses though manure to the surface for release. The diffusion process is mainly affected by the ammonia concentration difference in the manure. Emission of ammonia gas (NH₃) into air occurs at the surface of manure and the process and rate of transformation from animal manure is affected by surface area, surface airflow, air temperature, relative humidity, and ammonia air concentration (Ni, 1999). High-speed airflow reduces the still air above the manure and significantly increases ammonia emission. Small surface area, little disturbance of the manure, and high ammonia concentration in air are all beneficial conditions to reduce ammonia emission.
|Figure 1. Major sources of ammonia emissions from animal feeding operations: (a) animal buildings; (b) manure storages; and (c) land applications of manure.|
|Figure 2. The USEPA estimation of ammonia emissions from animal feeding operations.|
Health impact of ammonia (NH₃) emission
Ammonia emission causes high ammonia levels inside animal production buildings, especially in winter months when the buildings operate at low ventilation rates for temperature control and conservation of energy. Studies have found ammonia gas (NH₃) concentrations are typically 5–18 ppm in confinement swine barns, 3–8 ppm in open dairy barns, and 10–100 ppm in confined poultry facilities (Zhao et al. 2007; Arogo et al., 2001).
Ammonia present in indoor air is considered a health hazard. Due to its high chemical reactivity, ammonia gas (NH₃) is a very strong irritant. For humans, ammonia (NH₃) inflames eyes and lungs, even at low concentrations. People begin to detect odors at 5–50 ppm. Irritation to mucous surfaces occurs at 100–500 ppm. Immediate irritation of eyes, nose and throat occurs at 400–700 ppm. Severe eye irritation, coughing and frothing at the mouth, which could be fatal, occur at 2000–3000 ppm. Respiratory spasm and rapid asphyxia may occur at 5000 ppm. It is rapidly fatal at 10,000 ppm. The primary features after NH₃ exposure are summarized in Table 1 (ATSDR, 2004).
|Table 1. Reactions of humans to different levels of NH₃ concentration|
|Concentration (ppm)||Signs and symptoms|
|50||Irritation to eyes, nose and throat (2 hour exposure)|
|100||Rapid eye and respiratory tract irritation|
|250||Tolerable by most persons (30–60 minute exposure)|
|400–700||Immediately irritating to eyes and throat|
|>1500||Pulmonary oedema, coughing, laryngospasm|
|2500–4500||Fatal (30 minutes)|
|5000–10,000||Rapidly fatal due to airway obstruction|
For animals, the occurrence of ascites, gastrointestinal irritation, and respiratory diseases has been correlated with high ammonia concentrations (Carlie, 1984). The symptoms can be easily observed in poultry. At 10 ppm, trachea irritation was shown in turkeys. At above 20 ppm, increased rate of infection of Newcastle disease was found. At above 25 ppm, growth rate and feed conversion was impaired and the final body weight was reduced. At above 50 ppm, increased levels of keratoconjuctivitis and tracheitis have been observed. These trachea and lung lesions render the birds more susceptible to bacterial infections such as E. coli. At above 100 ppm, the chick mortality was increased significantly. High NH₃ concentrations have also been associated with a high incidence of contact dermatitis: foot, hock and breast burns. If the foot lesions are serious, lameness and leg problems may result. Many of these pathologies can be quite painful and stressful for the birds. Excessive mucous production, matted cilia, and deterioration of normal mucociliary apparatus were found in turkeys exposed to ammonia concentrations as low as 10 ppm for 7 weeks.
OSHA, the Occupational Safety and Health Administration, has an "8-hour exposure limit of 25 ppm and a short-term (15-minute) exposure limit of 35 ppm for ammonia in the workplace" (ATSDR, 2004). NIOSH, National Institute for Occupational Safety and Health, recommends that ammonia concentration in workrooms be limited to 50 ppm for 5 minutes of exposure (ATSDR, 2004).
Environmental impact of ammonia (NH₃) emission
After emitted, ammonia gas has a very short atmospheric lifetime and is usually deposited in wet precipitation (rainfall) and dry fall near its point of origin (Schlesinger, 1991). A nutrient imbalance in the soil can be harmful to some crops and aquatic systems. (NRC, 2003). Ammonium compounds deposited into soil and water systems can cause soil acidification and eutrophication of surface water (Van Breemen et al., 1982), as has occurred as acidic conditions in the Rocky Mountain and toxic algae blooms in Lake Erie.
In addition, ammonia can easily combine with other atmospheric pollutants forming more harmful aerosols. Most commonly, ammonia gas (NH₃) present in the lower atmosphere can react with sulfuric and nitric acid in the air and form small ammonium aerosol particles ((NH₄)₂SO₄, NH₄NO₃). It was found that ammonium aerosols account for 47% of fine particulate matter (PM2.5) (Anderson et al., 2003). After NH₃ is converted to ammonium aerosols, their lifetime increases up to 15 days and they can get deposited at larger distances (Aneja et al., 2000). The fine aerosol particles can form haze and affect atmosphere visibility. They can also penetrate human and animal respiratory passages and cause health problems.
Ammonia emission is a natural process. However, too much ammonia can cause health concerns for humans and animals. Ammonia emission and dispersion result in environmental impacts. Understanding ammonia emission generation and dispersion process can lead to effective and economically feasible best management practices (BMPs) for animal feeding operations. Use of BMPs will not only contribute to improved health and environment, but also conserve nitrogen to improve manure fertilizer values.
The fact sheet has been reviewed by Karen Mancl, Professor, and Harold Keener, Professor Emeritus, Food, Agricultural and Biological Engineering, The Ohio State University.
Other resource materials
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