When in gaseous form, ammonia has a short atmospheric lifetime of about 24 hours and usually deposits near its source (the majority of gaseous ammonia is depositied within 700 -1000 m of feedlot parimeters; 29). In particulate form ammonia can travel much further impacting a larger area. Both gaseous and particulate ammonia contribute to eutrophication of surface waters, soil acidification, fertilization of vegetation, changes in ecosystems (5),and smog and decreased visibility in cities and pristine areas.
Since ammonia is one of the only basic species in the atmosphere, it readily reacts with strong acidic species in the atmosphere such as nitric and sulfuric acids, which are byproducts of combustion process including vehicle and industrial sources, to form ammonium salts, also known as fine particulate matter or PM2.5.
Due to their small diameter (less than 2.5 microns (µm)) and increased atmospheric lifetime of 15 days, these particulates are able to travel long distances before being dry or wet deposited to the ground surface. This allows them to travel from rural areas to urban locations where they mix and build up in the atmosphere leading to smog or transportation to other areas. In Colorado transport of these particulates from urban areas to pristine mountain regions, such as Rocky Mountain National Park, has been documented. Deposition of these N rich particulates in the Park has caused changes in the Park's vegetation, lakes, and natural ecosystems.
- Eutrophication is a result of nutrient pollution (from deposition or run-off) into natural waters (creeks, rivers, ponds, or lakes). Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality. In aquatic environments, enhanced growth of choking aquatic vegetation or algal blooms disrupt normal functioning of the ecosystem, causing problems such as a lack of oxygen in the water, needed for fish and other aquatic life to survive. The water then becomes cloudy, colored a shade of green, yellow, brown, or red.
- Soil Acidification
- When ammonia reaches the soil surface, it usually reacts with water in the soil and is converted into its ionic form, ammonium (NH4+) and absorbes to the soil. The ammonium in the soil eventually disassociates or is nitrified into nitrite (NO2-) or nitrate (NO3-) by nitrifying bacteria, releasing H+ ions into the soil (3, 4). If not taken up by biomass and converted to methane, the surplus H+ ions eventually lead to the formation of an acidic soil environment. The nitrogen left over in the soil will either be taken up by plants, stored in the soil, returned to the atmosphere, or will be removed from the soil in runoff or leaching (3).
- Fertilization of Vegetation
- Fertilization of vegetation by ammonia occurs in much the same way as applying fertilizer to the soil; however, in this case ammonia gas from the air deposits on the leaf or soil surface at the base of the plant and is taken up by the plant. Changes in plant growth can then occur, similar to those resulting from fertilization. In a grass plains environment, changes may be subtle; however, in natural or mountain areas, changes in plant species may be more obvious, promoting weedy plants while choking out native plants and wild flowers or promoting grasses and sages.
- Changes in Ecosystems
- An ecosystem is a natural system consisting of plants, animal, and other microorganisms functioning together in a balanced relationship. Changes in ecosystems due to ammonia deposition occur through a combination of all the above mentioned processes. When changes in ecosystems occur, the natural balance of a system is disrupted and fragile plant and animal species can be replaced by non-native or N-responsive species. The disruption of an ecosystem can cause it to adapt by changing (positive or negative outcome), or a disruption may lead to the extinction of the ecosystem.
- Smog and Decreased Visibility
- When ammonia combines with NOx and SOx emissions from industrial and vehicle combustion processes it forms fine particulates. These fine particulates (also known as PM2.5) are a contributor to haze/smog in cites and decreased visibility (haze) in pristine areas. Smog is also a human health issue leading to an increased rate of respiratory and heart diseases.
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Ammonia effects human and animal health both as a gas and as a particulate. The particulate form of ammonia has broader implications for the general public, where as the gaseous form is a localized concern for the health of animals and agricultural workers.
When in fine particulate (PM2.5) form, ammonium particles pose a risk to human health. Such small diameter particles are able to be respired and travel deep into lung tissue to the alveoli causing a variety of respiratory ailments such as bronchitis, asthma, coughing, and farmers lung. The particulate form of ammonia (PM2.5) is usually found in urban or suburban areas where ammonia gas from agriculture (and other sources) has undergone chemical reaction with urban emissions such as NOx and SOx and formed PM2.5 leading to smog formation.
Ammonia gas is a highly hydrophilic base that has irritant properties when inhaled which, when combined with water, can injure and burn the respiratory tract (42). The base form of ammonia, ammonium hydroxide, dissolves in the water of mucus membranes, hydrolyzes, and rapidly irritates tissues due to the high pH that results (43). Ammonia can also alter the uptake of oxygen by hemoglobin due to the increase of pH within the blood (42), which leads to decreased oxygenation of tissues, and decreased metabolic function.
Due to the side effects of ammonia gas exposure over 25 ppm, the American Conference of Governmental Industrial Hygienists (ACGIH) has recommended an 8 hour maximum exposure limit of 25 ppm to protect against the chronic effects of ammonia exposure. A 15 min short-term exposure limit of 35 ppm has been established by ACGIH and also adopted by OSHA to reduce irritant effects of ammonia exposure (i.e. eye and upper respiratory tract irritation). However, due to possible cumulative health effects over time, the recommended daily long-term occupational exposure limit of ammonia for agricultural workers is 7 ppm (44) , and 300 parts per billion (ppb) for community exposure (community exposure must be stricter because communities contain very susceptible people such as the elderly and children) (45). At moderate concentrations (50 to 150 ppm), ammonia exposure can lead to eye, throat and skin irritation as well as cough and mucus buildup. Prolonged exposure at this level can result in the transfusion of ammonia from the alveoli into the bloodstream and a subsequent disruption of oxygen uptake by hemoglobin. At high concentrations (>150 ppm) ammonia can scar lung tissue, cause lower lung inflammation and pulmonary edema. Exposure to high concentrations of ammonia (500 to 5000 ppm) will cause death in a relatively short time period from prevention of oxygen uptake by hemoglobin (45). These levels are rarely found near livestock operations, but may occur in closed manure storage facilities and poorly ventilated buildings where ammonia concentrations can accumulate.
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