The Clean Air Act of 1955 established specific National Ambient Air Quality Standards (NAAQS) for six compounds: carbon monoxide, ozone, particulate matter, sulfur dioxide, nitrogen oxides, and hydrocarbons. Subsequent reauthorization and amendments (especially in 1970) provided for uniform air quality standards and control of emissions from existing facilities. That is, the regional U.S. Environmental Protection Agency offices or individual state regulatory agencies must monitor air quality, and design and implement plans to improve air quality to NAAQS levels.
The Clean Air Act Amendment of 1990 (Pub. Law 101-549) also included several provisions of concern to producers of agricultural products. The most immediate of these concerns are the contribution of manure decomposition to ammonia emissions and the impact of manure handling on fugitive dust.
Particulate Matter
Particles of solid or liquid material suspended in air can cause eye and throat irritation and hamper visibility. In 1997 the U.S. Environmental Protection Agency issued a new standard for the Clean Air Act concerning particulate emissions. The new standard revised the air quality standard for particulate matter (PM) from PM10 to PM2.5. PM10 had been in effect since 1978. PM2.5 concerns particles 2.5 µm in aerodynamic diameter or less. The new standard was challenged in Fed- eral court and the D.C. Circuit ruled that EPA had overstepped its authority in issuing the new PM2.5 standard. In a 9 to 0 decision the Supreme Court revised the D.C. Circuit decision and re- manded the remaining issues back to the D.C. Circuit. By a 3 to 0 decision in 2002, the U.S. Court of Appeals for the D.C. Circuit ruled that EPA did not overstep its authority and the new standards were not arbitrary nor unreasonable.
Therefore, the particulate standard is PM2.5. In developing PM2.5, human health takes precedence over the cost of implementation. As enacted, ammonium nitrate — which is created by photochemical reaction between ammonia and nitric acid — will become a larger part of the total problem since the resulting particles are larger than 2.5 µm.
Reducing the formation of particulate matter benefits air quality — and everyone benefits from cleaner air. So even without regulations, growers will likely do whatever they can to reduce ammonia emissions, that is, to reduce the moisture content of litter and control litter pH. Indeed, they have — sometimes for other reasons — already adopted management practices that will help achieve this goal, such as maintaining waterers in good condition, applying treatments to litter (i.e., bedding materials for ammonia control), and composting litter and mortalities.
Technological controls, such as installing equipment to scrub ammonia before the air is vented from buildings, may be more costly than the problem warrants. Some technological controls may be helpful; however, care should be taken to ensure that a technology devised to control a specific problem, such as the generation of methane gas, is not expected to remedy other problems. For example, covered lagoons will not do much to solve the fugitive dust problem.
It is important for growers to be aware of regulatory concerns and evaluate their management practices and prospective technologies holistically. The best practices are effective, economical, and do no harm to the environment.
Gaseous Emissions
Goals of the 1990 Clean Air Act include reducing emissions to the air that cause acid rain and protecting stratospheric ozone. Thus, ammonia (NH3) volatilization from animal and other agricultural operations is subject to increased scrutiny.
A variety of gases are generated during the decomposition of poultry wastes. Under aerobic conditions, carbon dioxide (CO2) is the principal gas produced; under anaerobic conditions, the primary gases are methane (CH4) and (CO2). About 60 to 70 percent of the gas generated in an anaerobic lagoon or pit is methane and about 30 percent is (CO2). Trace amounts of more than 75 other volatile compounds have been identified from degrading animal waste, including mercaptans (the odor generated by skunks and the smell introduced in natural gas are in the mercaptan family), aromatics, sulfides, various esters, carbonyls, and amines.
Methane, Carbon Dioxide, Ammonia, and Hydrogen Sulfide
The gases of most interest and concern in poultry waste management are methane, carbon dioxide, ammonia, and hydrogen sulfide. The following paragraphs summarize the most significant characteristics of these gases.
Methane
Methane gas forms during the breakdown of animal wastes, if the decomposition process is anaerobic. Because methane is quite explosive, extreme care is required when attempting to generate and capture this gas for on-farm use.
Further, methane emissions from “rice and livestock production” and from “all forms of waste management . . . including storage, treatment, and disposal” are specifically mentioned as a concern in the 1990 Clean Air Act. Methane accounts for about 18 percent of the greenhouse gases that contribute to ozone depletion.
Carbon Dioxide
Carbon dioxide can be an asphyxiant when it displaces normal air in a confined facility. Because CO2 is heavier than air, it remains in a tank or other well-sealed structure, gradually displacing the lighter gases. With high-density housing, gas and particulate levels may increase, and control becomes more difficult.
Carbon dioxide can increase substantially inside the poultry house, depending on the number of birds producing it. Continued monitoring of temperature, air removal rate, and manure moisture content is required to maintain proper carbon dioxide concentrations.
Nitrous Oxide and Ammonia
Ammonia is primarily an irritant and has been known to create health problems in animal confinement buildings. Irritation of the eyes and respiratory tract are common problems from prolonged exposure to this gas. It is also associated with soil acidification processes.
Ammonia concentration in broiler houses has increased in the past few years. The primary reason is that ventilation rates are reduced to conserve heat in the winter months. Research also shows that dust particles serve as an ammonia transport mechanism, so venting to the outside may lead to odors near the house and contribute to overly dry litter inside the house.
Ammonia concentration increases with increasing pH, temperature, and litter moisture content. It is desirable to maintain litter moisture in a production house below 30 percent for ammonia control. Studies indicate that ammonia increases bird susceptibility to Newcastle disease and decreases feed intake and egg production.
Nitrous oxide is produced during the breakdown of nitrogen fertilizers in soil, animal wastes, and nitrate-contaminated groundwater, although its major source is the burning of fossil fuels. Nitrous oxide accounts for about 6 percent of the greenhouse gases related to human activity.
Hydrogen Sulfide
Hydrogen sulfide is deadly. Humans and farm animals have been killed by this gas after falling into or entering a storage tank or building in which a storage tank was being agitated. Although only small amounts of hydrogen sulfide are produced as compared to other major gases, this gas is heavier than air and becomes more concentrated over time.
Hydrogen sulfide has the distinct odor of rotten eggs. Hydrogen sulfide deadens the olfactory nerves (the sense of smell); therefore, even if the smell of rotten eggs appears to have disappeared, an area may still be contaminated with this highly poisonous gas. Forced-air ventilation or an exhaust system helps prevent gas poisoning. Otherwise, evacuate the area until the gas can be removed.
Methods used to capture and treat these gas emissions will have the additional advantage of reducing odor. They include the use of covered storage pits or lagoons, soil adsorption beds and filter fields, and applying litter with soil incorporation. Technological controls are possible, for example, installing packed bed scrubbers in the poultry house or composting area (or wherever the manure is processed. Newer methods include burning the manure to produce energy, which is discussed in AT/2.
Issues Not Directly Related to Air Quality
Nuisance issues — odor, flies, dust, and noise — are generally regulated at the state or local level. They can be, but are not usually related to air quality standards, even though many citizen complaints and civil suits brought against livestock and poultry operators may reference such standards. These problems are more often related to improper or mismanaged burial pits, emissions from incinerators, and land applications of poultry waste. They are intensified by increasing urbanization, unanticipated adverse weather conditions, and specific, often seasonal, activities in the production cycle. Other fact sheets in this handbook deal with these potential problems.
Where to Go for Help
Information on achieving air quality standards and managing air quality problems related to poultry production facilities is available from the U.S. Department of Agriculture, U.S. Environmental Protection Agency, and the U.S. Department of Energy. Poultry associations and state air-water quality agencies can also help.
References
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