1
Introduction

This interim report provides the U.S. Environmental Protection Agency (EPA), the U.S. Department of Agriculture (USDA), other federal and state agencies, the animal feeding industry, and the general public an initial assessment of the methods and quality of data used in estimating air emissions from animal feeding operations (AFOs as defined by EPA; see Appendix B). These emissions, their impacts, and the methods used to mitigate them affect the health and well-being of individual farms, the agricultural economy, the associated environments, and people. The scientific aspects of this broad issue deserve attention, both in the near term as possible revisions of federal water quality regulations are being considered, and in the longer term as attention shifts to ways to mitigate air emissions.

The stakes in this issue are large. More and more livestock are raised for at least part of their lives in AFOs in response to economic factors that encourage further concentration. The impacts on the air in surrounding areas have grown to a point where further actions to mitigate them appear likely. The overall study, of which this interim report is part, has been requested to help ensure that choices among alternatives are made on the basis of information that meets the tests of scientific accuracy.

The committee has been sensitive to the fact that its findings are not being written on a blank slate. The types of actions that might ultimately result from this and other reports could include various kinds of regulation, public incentive approaches, and technical assistance, all of which are already being used to some extent by the states and federal agencies. The committee also notes that this interim report will be supplemented by a final report in another six months, and that some of the discussions of possible approaches to



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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations 1 Introduction This interim report provides the U.S. Environmental Protection Agency (EPA), the U.S. Department of Agriculture (USDA), other federal and state agencies, the animal feeding industry, and the general public an initial assessment of the methods and quality of data used in estimating air emissions from animal feeding operations (AFOs as defined by EPA; see Appendix B). These emissions, their impacts, and the methods used to mitigate them affect the health and well-being of individual farms, the agricultural economy, the associated environments, and people. The scientific aspects of this broad issue deserve attention, both in the near term as possible revisions of federal water quality regulations are being considered, and in the longer term as attention shifts to ways to mitigate air emissions. The stakes in this issue are large. More and more livestock are raised for at least part of their lives in AFOs in response to economic factors that encourage further concentration. The impacts on the air in surrounding areas have grown to a point where further actions to mitigate them appear likely. The overall study, of which this interim report is part, has been requested to help ensure that choices among alternatives are made on the basis of information that meets the tests of scientific accuracy. The committee has been sensitive to the fact that its findings are not being written on a blank slate. The types of actions that might ultimately result from this and other reports could include various kinds of regulation, public incentive approaches, and technical assistance, all of which are already being used to some extent by the states and federal agencies. The committee also notes that this interim report will be supplemented by a final report in another six months, and that some of the discussions of possible approaches to

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations estimating air emissions are being left for that report as noted in relevant places in this interim report. The committee has answered the following sets of questions in the interim report within the confines of the Statement of Task (see Appendix A): What are the scientific criteria needed to ensure that reasonably appropriate estimates of emissions are obtained? What are the strengths, weaknesses, and gaps of published methods to measure specific emissions and develop emission factors that are published in the scientific literature? How should the variability due to regional differences, daily and seasonal changes, animal life stage, and different management approaches be characterized? How should the statistical uncertainty in emissions measurements and emissions factors be characterized in the scientific literature? Are the emission estimation approaches described in the EPA report Air Emissions from Animal Feeding Operations (EPA, 2001a) appropriate? If not, how should industry characteristics and emission mitigation techniques be characterized? Should model farms be used to represent the industry? If so, how? What substances should be characterized and how can inherent fluctuations be accounted for? What components of manure should be included in the estimation approaches (e.g., nitrogen, sulfur, volatile solids [see Appendix B])? What additional emission mitigation technologies and management practices should be considered? What criteria, including capital costs, operating costs, and technical feasibility, are needed to develop and assess the effectiveness of emission mitigation techniques and best management practices? Given the specific nature of the questions posed by EPA, the committee has not yet addressed some of the longer-term issues related to AFOs. To the extent possible, these will be addressed in the final report, which will build upon the findings of this interim report and include a more detailed response to the committee’s full Statement of Task (see Appendix A). The need for further discussion in the final report is indicated for some specific concerns in various places in this report. The topics to be covered in the final report fall in eight broad categories: (1) industry size and structure, (2) emission measurement methodology, (3) mitigation technology and best management plans, (4) short-and long-term research priorities, (5) model farm approaches, (6) human health and environmental impacts, (7) economic analyses, and (8) other potential air emissions of concern. The quality of data for estimating air emissions from AFOs is an issue throughout this report. The committee’s inclination at first was to refer only to data from peer-reviewed sources. It soon became evident that this would eliminate a number of references that were prepared and relied upon by federal and state agencies, including the EPA (2001a) report that the committee is

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations directed to review as part of its assignment. These reports sometimes rely on information from primary sources that have been peer reviewed, in which case they would meet the standard generally adopted by the committee. The committee decided that it would use results presented in these non-peer-reviewed or “gray literature” reports as long as it could determine that they reflected peer-reviewed sources. It also decided that it would clearly indicate instances where it believed that judicious use of non-peer-reviewed reports was needed. EPA may use information from this project in determining how it will approach regulating both air and water quality impacts of AFOs. Substantial emissions of nitrogen (N), sulfur (S), carbon (C), particulate matter (PM), and other substances from AFOs do occur and cannot be ignored. This interim report also makes reference to possible influences that regulations proposed by the EPA Office of Water may have on aggravating air emissions from AFOs. The EPA’s Office of Air and Radiation’s concern with the possible effect of water quality regulations on air emissions is well placed. Effects on air emissions of nutrient management practices currently recommended to protect water quality are generally unknown. In addition to potential conflicts between air quality and regulations aimed at improving water quality, state regulations based on inadequate air emissions information may lead to inappropriate actions. Better understanding of the reliability of air emissions estimates will help EPA and the states to assess the appropriateness of regulations. The potential effects on air emissions from changes in water quality regulations for AFOs will be difficult to predict, especially given the large number of AFOs in existence and the substantial number of animals involved. Changes induced through new water quality regulations could be either positive or negative in their effects on air quality. For example, the proposed water regulations may mandate nitrogen and phosphorus based comprehensive nutrient management plans (CNMPs). AFOs could be limited in the amount of manure nitrogen and phosphorus that could be applied to cropland. If there is a low risk of phosphorus runoff as determined by a site analysis, farmers may be permitted to overapply phosphorus. However, they will still be prohibited from applying more nitrogen than recommended for crop production. Many AFOs (those currently without CNMPs) likely will have more manure than they can use on their own cropland, and manure export may be cost prohibitive. Thus, AFOs will have an incentive to use crops and management practices that employ applied nitrogen inefficiently (i.e., volatilize ammonia) to decrease the nitrogen remaining after storage or increase the requirement for nitrogen on crop production. These practices could increase nitrogen volatilization to the air. AFOs with limited space to apply manure to fertilize their crops would have to adopt alternative management practices. Effects on air emissions of dispersal of manure across additional cropland (if available) must be considered. Although the transport of manure off-site reduces the emissions associated with that AFO,

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations it does not guarantee an overall reduction of emissions into the environment. The committee recognizes that the EPA Office of Air and Radiation, and Office of Water face a considerable task in drafting new regulations and evaluating proposed regulations in terms of their relative impacts on air and water quality. Finding 1: Proposed EPA regulations aimed at improving water quality may affect rates and distributions of air emissions from animal feeding operations. Regulations developed by the EPA’s Office of Air and Radiation for AFOs will be influenced in part by existing National Ambient Air Quality Standards (NAAQS; EPA, 2002). These standards define concentration limits for ambient concentrations of six criteria pollutants (carbon monoxie, nitrogen dioxide, ozone, lead, PM10, and sulfur dioxide) based on health effects. Exceedances of these standards can result in areas being classified as “nonattainment” areas. The state implementation plans (SIPs) subsequently approved by EPA are plans for bringing these areas into attainment. SIPs may include sources of pollutants targeted for reduction. These are usually regulated by decreasing the allowable emission rates established by the permit control at each source needed to meet the NAAQS. States can legislate more stringent ambient air quality standards within their boundaries. Several of the substances emitted from AFOs that are of concern in this report are not regulated under NAAQS; examples include ammonia, hydrogen sulfide, and odor. Developing SIPs for a region that contains AFOs may require knowledge of their air emissions. AFOs can differ significantly from each other in terms of construction, management, and operation. They can be widely distributed across the landscape or concentrated in geographic regions. To be effective, regulatory actions must ultimately account for emissions at the individual farm level and be based on information that can be used to attribute emissions to specific operations. Estimates of emissions at the state or regional level (e.g., across a watershed or river basin) may be sufficient to trigger the need for regulatory action. However, such actions, if needed, will ultimately depend on the ability to assign emissions to the individual operations that produce them. Application of remediation policies will in turn require knowledge of emissions from the individual components of AFOs. Finding 2: In order to understand health and environmental impacts on a variety of spatial scales, estimates of air emissions from AFOs at the individual farm level, and their dependence on management practices, are needed to characterize annual emission inventories for some pollutants and transient downwind spatial distributions and concentrations for others.

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations Estimating emissions of gases, PM, and other substances from AFOs is technically difficult. The variety of emissions; the different conditions under which they are emitted; the subsequent mixing, chemical reactions, and deposition following emission; the types and sizes of emitting operations; and the difficulty of obtaining representative samples all contribute to the challenge of accurately characterizing AFOs as emission sources. As reflected by EPA (2001a), an attempt was made to address the need for emissions estimates from individual AFOs (Finding 2) and to address the difficulty in characterizing AFOs as emissions sources by developing the concept of model farms. By judicious selection of criteria, emission factors obtained from the scientific literature for components of those model farms may allow for calculation of the desired estimate of annual mass emissions from a single AFO. To that end, the quality and lack of these data are discussed in detail in Chapter 2. The only remaining requirements would be assigning an individual AFO to a specific model farm category and an accounting of the animal units (AUs as defined by EPA and used throughout this report; see Appendix B) housed there. The approach outlined by EPA (2001a) could be interpreted as representing a compromise between the physical impracticality of installing monitoring equipment on every AFO (due to cost and the lack of standardized emission measurement methodologies that can be adopted for routine monitoring) and the growing public pressure to consider rural air quality as an integral part of resource management. The committee supports the proposition that it is impractical to consider installing monitoring equipment at every AFO. First, emissions from AFOs are not typical of point sources since there are usually few convenient centrally located points from which to monitor emissions. Second, determining source emissions from AFOs should not be confused with monitoring atmospheric concentrations of gases, PM, or other substances. Measurement of atmospheric concentrations of substances is an important component in determining emissions, but application of meteorological models with other complementary data are often necessary to back-calculate emission rates or fluxes for gases and PM. In addition, no standard methods have been developed for measuring source emissions that state agencies could adopt for monitoring individual operations, let alone advising individuals on deployment and measurement strategies, given the diversity in design and operation of AFOs. Routine monitoring of air quality is employed for compliance purposes in many industries (i.e., electrical power, automobiles); however such efforts are based on many years of research to develop models to predict the emission from these anthropogenic sources with some degree of confidence. A corresponding investment of time and resources has not been made in understanding emissions from biological systems such as AFOs; however these research measurements are sorely needed.

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations Finding 3: Direct measurements of air emissions at all AFOs are not feasible. Nevertheless, measurements on a statistically representative subset of AFOs are needed and will require additional resources to conduct. The committee also agrees that characterizing AFOs in terms of their production components (e.g., model farms) may in general be a plausible approach for developing estimates of air emissions. EPA (2001a) developed a set of 23 model farms (see Appendix D) intended to represent the majority of commercial-scale AFOs. Each model farm included three variable elements: a confinement area, manure management system, and land application method. The manure management system was subdivided into solid separation and manure storage activities. A number of arguments exist to support an approach such as that outlined by EPA (2001a) with the creation of model farms. Most AFOs can be subdivided according to different manure management systems that are in turn constructed of individual processing steps. Animal housing units are often of a specified design depending on animal age and type. Although housing units may vary in design among farms, within an individual farm the housing units are generally uniform with respect to size, ventilation, and number of days animals are kept in each house. Feed formulations are also generally controlled uniformly as a function of animal age and stage of production. Animal growth across its life is often predicted through the use of models. Variations in ambient temperature due to seasonal changes no doubt cause changes in housing emissions due to the need to increase or decrease ventilation to remove or conserve heat. Ventilation protocols designed to control temperature and humidity may help to decrease concentrations of air emissions and maintain animal health. Thus, on a yearly basis, it may be possible to account for these seasonal variations. It could be argued that expressing emissions on a yearly basis would also tend to average out rotations of animals in and out of housing units; animal age varies between housing units on many AFOs. Emissions of gases such as ammonia (NH3) from manure treatment lagoons are dictated to a large extent by the ambient air temperature (through its influence on lagoon water temperature), lagoon pH, wind speed across the lagoon, and dissolved ammonium ion (NH4 +) concentration and are relatively independent of week-to-week variations in loading of animal manure. Changes in NH3 emissions due to changes in ambient temperature could conceivably be accounted for through the generation of regression models relating temperature, pH, and dissolved ammonium ion concentration. Similar examples could be given for other types of manure management systems; it is reasonable to assume that individual processing steps within a given manure management system could be characterized by single emission factors that when combined, would lead to a viable estimate of emissions for each type of model farm. The only

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations limitation in the approach is the lack of accurate emission factors based on field data for the individual processing steps and interactions among these steps. In opposition to the above statements are the intuitive arguments that AFOs are complicated systems with inherent variability because of differences in physical design and the fact that AFOs are biological systems with daily, seasonal, and probably yearly cycles. The biological complexity of AFOs exists at both the macro- and the microscales. The macroscale may include the various growth stages of animals being produced, with changes in feed formulation, consumption, productivity, and manure produced. The microscale may include microbial activity within the animal and in excreted animal manure; all microbial processes depend to some degree on changes in temperature, oxygen concentrations, and moisture content. Measured emission rates will necessarily have a component of uncertainty that will carry over to emission factors generated from them. Deriving an estimate of this uncertainty is necessary in order to compare estimated emissions among individual AFOs and to compare the emissions from a single AFO to regulatory limits. A substantial body of research shows that the air emissions from AFOs depend on a variety of factors that vary among the different kinds of operations. It is reasonable to expect that there are particular sets of factors, to be established with statistical techniques, that will be most useful in estimating air emissions for each kind of operation. However, the committee believes that the model farm construct currently outlined (EPA, 2001a) has not identified all of the factors necessary to characterize emissions from individual AFOs. Finding 4: Characterizing feeding operations in terms of their components (e.g., model farms) may be a plausible approach for developing estimates of air emissions from individual farms or regions as long as the components or factors chosen to characterize the feeding operation are appropriate. The method may not be useful for estimating acute health effects, which normally depend on human exposure to some concentration of toxic or infectious substance for short periods of time. ANIMAL PRODUCTION In 1995, at any given time there were approximately 13 billion chickens, 1.3 billion cattle, and 0.9 billion pigs worldwide; of these, 1.6 billion chickens, 0.1 billion cattle, and 0.06 billion pigs were located in the United States (Food and Agriculture Organization, 2002). The U.S. stocks sustained the production of 11.5 Tg of chicken meat, 11.6 Tg of beef and veal, and 8.1 Tg of pork. These products are important sources of calories and protein; in 1993, they supplied 28 percent of the calories and 64 percent of the protein consumed

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations by humans in the United States (Council for Agricultural Science and Technology, 1999). In addition to producing food, animals also produce waste. In 1997, 1 x 1012 kg (103 Tg) of manure was excreted in the United States, with confined animals producing about 40 percent of it (Kellogg et al., 2000). This report addresses the issue of air emissions from AFOs with a special focus on the gases ammonia (NH3), nitric oxide (NO), hydrogen sulfide (H2S), nitrous oxide (N2O), and methane (CH4); the general class of materials designated volatile organic compounds (VOCs); odor-causing compounds; and the aerosol classes PM2.5 and PM10 (particulate matter having aerodynamic diameters less than 2.5 and less than 10 micrometers (µm), respectively). In the remaining sections estimates of global emissions are presented based on reviews from a number of sources, often using emission factors. Given the uncertainties in emission factors, these global emissions also have uncertainties, which are limited by constraints on global budget terms (such as loss rates). Estimates of aggregated emissions rates from all sources can be at least partially validated by measurement of spatial and temporal differences in ambient air concentrations. Accuracy of attribution of total emissions to individual sources is limited by incomplete lists of the sources, and errors in assumed emission factors for each source. The source-specific estimates provided in the following sections are subject to these limitations but are presented to give the reader a general sense of each source's importance. EMISSIONS FROM ANIMAL FEEDING OPERATIONS Ammonia The nitrogen in animal manure can be converted to ammonia by a combination of mineralization, hydrolysis, and volatilization (Oenema et al., 2001). On a global scale, animal farming systems emit to the atmosphere ~20 Tg N/yr as NH3 (Galloway and Cowling, 2002), about 65 percent of total NH3 emissions from terrestrial systems (van Aardenne et al., 2001). In the United States, about 6 Tg N/yr is consumed by animals in feed, of which about 2 Tg N/yr is emitted to the atmosphere as NH3 and about 1 Tg N/yr is consumed by humans in meat products (Howarth et al., 2002). Once emitted, the NH3 can be converted rapidly to ammonium (NH4+) aerosol by reactions with acidic species (e.g., HNO3 [nitric acid], H2SO4 [sulfuric acid], NH4HSO4 [ammonium bisulfate]). Gaseous NH3 is removed primarily by dry deposition; aerosol NH4+ is primarily removed by wet deposition. The residence time of NH3 and NH4+ in the atmosphere is on the order of days, and they can be transported hundreds of kilometers. As an aerosol, NH4+ contributes directly to PM2.5 and, once removed, contributes to ecosystem fertilization, acidification, and

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations eutrophication. Once NH3 (or NO) is emitted to the atmosphere, each nitrogen atom can participate in a sequence of effects, known as the nitrogen cascade, in which a molecule of NH3 can, in sequence, impact atmospheric visibility, soil acidity, forest productivity, stream acidity, and coastal productivity (Galloway and Cowling, 2002). Excess deposition of reactive nitrogen (either NH3 - NH4+ or nitrate) can reduce the biodiversity of terrestrial ecosystems (National Research Council, 1997). Nitric Oxide Although nitric oxide was not specifically addressed by EPA (2001a), the committee believes it should be included in this report because NO is a precursor to photochemical smog and ozone (O3), and is oxidized in the atmosphere to nitrate, which along with NH3 contributes to both fine PM and excess nitrogen deposition. The environmental consequences of nitrate deposition are similar to those of NH3. NO and nitrogen dioxide (NO2) are rapidly interconverted in the atmosphere and are referred to jointly as NOx. A small fraction of NH4 + and other reduced nitrogen compounds from animal manure is converted to NO by microbial action in soils. Under the new EPA regulation for ozone (0.08 part per million (ppm) 8-hour average), more rural areas will likely violate the standard, and NO emissions from agricultural soils will become more important. Key variables include land use, the amount of NH4 + and nitrate being applied to soils, and the emission rate. Oxides of nitrogen are the key precursors to tropospheric O3 (part of photochemical smog). NOx can be incorporated into organic compounds such as peroxyacetyl nitrate (PAN) or further oxidized to nitric acid. The sum of all oxidized nitrogen species (except N2O) in the atmosphere is often referred to as NOy. The residence time of NOy is on the order of 1 day, unless it is lofted into the free troposphere where the lifetime is longer and environmental effects are more far reaching. Gas-phase HNO3 can be converted to nitrate aerosol, a contributor to PM2.5, and reduced visibility. Nitric acid and particulate nitrate are removed from the atmosphere by wet and dry deposition with the ecological consequences outlined earlier. Anthropogenic activities account for most of the NO released into the atmosphere, with combustion of fossil fuels representing the largest source (van Aardenne et al., 2001). Nitrification in aerobic soils appears to be the dominant pathway for agricultural NO release, with only minor emissions directly from livestock or manure. The contribution of soil emissions to the global oxidized nitrogen budget is on the order of 10 percent. Where corn is grown extensively, the contribution is much greater, especially in summer; Williams et al. (1992) estimated that contributions from soils amount to about 26 percent of the emissions from industrial and commercial processes in Illinois and may

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations dominate emissions in Iowa, Kansas, Minnesota, Nebraska, and South Dakota. The fraction of fertilizer nitrogen released as NOx depends on the mass and form of nitrogen (reduced or oxidized) applied to soils, the vegetative cover, temperature, soil moisture, and agricultural practices such as tillage. Hydrogen Sulfide Hydrogen sulfide is produced in anaerobic environments from the decomposition of sulfur-containing organic matter and the reduction of sulfate. It is emitted during manure decomposition and by the reduction of sulfate in feeds and water. On a global basis, 0.4 - 5.6 Tg S/yr of reduced sulfur gases (mostly H2S and (CH3)2S [dimethyl sulfide] are emitted from land biota and soils (Penner et al., 2001). Most H2S in the atmosphere is oxidized to sulfur dioxide (SO2), which is then either dry deposited or oxidized to aerosol sulfate and removed from the atmosphere primarily by wet deposition. The residence time of H2S and its reaction products is on the order of days. While the terrestrial emissions of H2S are small compared to SO2 from fossil fuel combustion (90 Tg S/yr), emissions from AFOs may be important on a local and regional basis. Their effects include an impact on occupational health and a contribution to regional sulfate aerosol loading. H2S is regulated (differently) in a number of states (Table 1-1). EPA does not currently list it as a hazardous air pollutant. Because toxic effects depend on both concentrations and exposure times, the periods over which measurements are to be averaged are also shown in Table 1-1. TABLE 1-1. Current Hydrogen Sulfide Standards in Various States State Standard (ppb) Averaging Period California 8a Not specified California 30 1 hr Illinois 10 8 hr Minnesota 7 3 months Minnesota 60 1 hr New York 0.7 1 yr a Termed the chronic reference inhalation standard. Units are parts per billion. SOURCE: Environmental Health Sciences Research Center (2002)

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations Nitrous Oxide Nitrous oxide is emitted to the atmosphere from animal manure via the processes of nitrification and denitrification. Biogenic sources dominate global N2O emissions, and of the total 18 Tg N/yr, anthropogenic processes account for about 8.1 Tg N/yr. Of these, cattle feedlots are thought to contribute about 2.1 Tg N/yr and agricultural soils receiving manure about 4.2 Tg N/yr (Prather et al., 2001). N2O is lost from the troposphere primarily by diffusion into the stratosphere, where it is lost to photolysis and other processes. Once emitted, N2O is globally distributed because of its long residence time (~100 years) and contributes to both tropospheric warming and stratospheric ozone depletion. Methane Methane is produced by microbial degradation of organic matter under anaerobic conditions. Biogenic sources dominate the global CH4 budget with roughly 60 percent of the total being anthropogenic. Of the global source strength, 600 Tg CH4/yr, ruminants (domesticated and wild) contribute about 90 Tg CH4/yr, landfills about 40 Tg CH4/yr, and rice cultivation about 60 Tg CH4/yr (Prather et al., 2001). A small portion of U.S. CH4 emissions come from crop residue burning, wildfires, and wetland rice cultivation. The role of AFOs, especially anaerobic manure lagoons, remains uncertain. Because of the long residence time (~8.4 years) CH4 becomes distributed globally. Its primary loss mechanism in the atmosphere is conversion to CO. Methane is a greenhouse gas and contributes to global warming (National Research Council, 1992). The primary source of CH4 in livestock production is ruminant animals. Globally, domesticated ruminants produce about 80 Tg annually, accounting for about 22 percent of CH4 emissions from human-related activities (Gibbs et al. 1989). Livestock ruminants (sheep, goats, camel, cattle, and buffalo) have a unique, four-chambered stomach. In one chamber called the rumen, bacteria break down grasses and other feedstuff to generate methane as one of several by-products. Its production rate is affected by several factors (quantity and quality of feed, animal body weight, age, and amount of exercise) and varies among animal species and among individuals of the same species (Leng, 1993). An adult cow produces between 80 and 120 kg of CH4 annually. In the United States, cattle emit about 6 Tg CH4/yr, equivalent to about 4.5 Tg C/yr. Lerner et al. (1988) estimated that of the annual global production of 400 to 600 Tg of CH4, enteric fermentation in domestic animals contributes approximately 65 to 85 Tg. Methane emissions from agricultural activities in the United States in 1999 were estimated at 9.1 Tg, 32 percent of total U.S. anthropogenic CH4. Ninety-five percent of CH4 emissions from agricultural activities came from livestock production. About 65 percent of these emissions could be traced to

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations enteric fermentation in ruminant animals, with the remainder attributable to anaerobic decomposition of livestock manure (DOE, 2000). The most important factor affecting the amount produced by manure is how it is managed, because certain types of storage and treatment systems promote an oxygen-depleted environment. Metabolic processes of methanogens lead to CH4 production at all stages of manure handling. Liquid systems tend to encourage anaerobic conditions and tend to produce significant quantities of CH4, while solid waste management approaches may produce little or none. Higher temperatures and moist conditions also promote CH4 production. Emissions from agriculture represented about 20 percent of U.S. CH4 emissions in 1999, with 6 percent from manure. From 1990 to 1999, emissions from this source increased by 8.0 Tg/yr CO2 (carbon dioxide) equivalent—the largest absolute increase of any of the CH4 source categories. The bulk of this increase—from swine and dairy cow manure—may be attributed to the shift in composition of the swine and dairy industries towards larger facilities using liquid management systems. Swine manure was estimated to produce 1.1 Tg/yr (CO2 equivalents), while beef and dairy produce 0.9 Tg/yr (CO2 equivalents) (EPA, 1999). Particulate Matter In the context of this report, particulate matter is grouped into two classes, PM10 and PM2.5. PM10 is commonly defined as airborne particles with aerodynamic diameters less than 10 µm. This definition is not precise, however, and the 10 µm diameter refers to the 50 percent cut diameter in a Federal Reference Method PM10 sampler (Federal Register, 1997), the aerodynamic diameter of a particle collected at 50 percent efficiency. Similarly, PM2.5 refers to the particles that are collected in a Federal Reference Method PM2.5 sampler (Federal Register, 1997) that has a 50 percent cut diameter of 2.5 µm. NAAQS are set for both PM10 and PM2.5 (Table 1-2). AFOs can contribute directly to PM through several mechanisms, including direct emissions from mechanical generation and entrainment of mineral and organic material from the soil and manure or indirect emissions of NO and NH3 that can be converted to aerosols through reactions in the atmosphere. Ammonium may be a major component of fine particulate matter over much of North America. The effective aerodynamic equivalent diameter of particulate matter is critical to its health and radiative effects. PM2.5 is targeted because its constituents have the greatest impact on human morbidity and mortality and are most effective in attenuating visible radiation. PM2.5 can reach and be deposited in the smallest airways (alveoli) in the lung, whereas larger particles tend to be deposited in the upper airways of the respiratory tract (National Research Council, 2002). Particles produced by gas-to-particle conversion

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations TABLE 1-2. National Air Quality Standards for Particulate Matter Particle Sizea Standard (µg/m3) Averaging Period PM10 50 1 yr   150 24 hr PM2.5 15 1 yr   65 24 hr aPM10 and PM2.5 refer to particulate matter with aerodynamic diameters up to 10 and up to 2.5 µm, respectively. SOURCE: EPA (2002) generally fall into the PM2.5 size range. Key variables affecting the emissions of PM10 include the amount of mechanical and animal activity on the dirt or manure surface, the water content of the surface, and the fraction of the surface material in the size range. For PM2.5, key variables affecting the emissions include the net release of precursors such as NO and NH3. Volatile Organic Compounds Volatile organic compounds (VOCs) are organic compounds that vaporize easily at room temperature. They include fatty acids, nitrogen heterocycles, sulfides, amines, alcohols, aliphatic aldehydes, ethers, p-cresol, mercaptans, hydrocarbons, and halocarbons. The majority of these compounds participate in atmospheric photochemical reactions, while others play an important role as heat-trapping gases (King, 1995). In 1993, VOC emissions from the San Bernardino Basin from livestock manure were estimated to be 12 tons per day (South Coast Air Quality Management District, 1993). Total emissions of VOCs from all sources in the United States were 30.4 Tg/yr in 1970 and 22.3 Tg/yr in 1995 (EPA, 1995a). Emission of VOCs from AFOs may cause significant economic and environmental problems. The major constituents that have been qualitatively identified include organic sulfides, disulfides, C4 to C7 aldehydes, trimethylamine, C4 amines, quinoline, dimethylpyrazine, and C3 to C6 organic acids in addition to lesser amounts of C4 to C7 alcohols, ketones, aliphatic hydrocarbons, and aromatic compounds. Some may irritate the skin, eye, nose, and throat on contact and the mucous membranes if inhaled. VOCs can also be precursors to O3 and PM2.5. VOCs that cause odors can stimulate sensory nerves to cause neurochemical changes that might influence health by compromising the immune system. Odors associated with VOCs can also trigger memories linked to unpleasant experiences, causing cognitive and emotional effects such as stress. At high levels of exposure, some VOCs are carcinogenic or can cause central nervous system disorders such as drowsiness and stupor.

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations However, the effects of air emissions from AFOs on public health are not fully understood or well studied. Greater mood disturbance (Schiffman et al., 1995) and increased rates of headaches, runny nose, sore throat, excessive coughing, diarrhea, and burning eyes have been reported by persons living near swine operations in North Carolina (Wing and Wolf, 2000). Thu et al. (1997) observed similarities between the pattern of symptoms among community residents living near large swine operations and those experienced by workers. Caution must be exercised in interpreting the studies because environmental exposure data were not reported. Odor Odor is complex both because of the large number of compounds that contribute to it (including H2S, NH3, and VOCs), and because it involves a subjective human response. Schiffman et al. (2001) identified 331 odor-causing compounds in swine manure. Though research is under way to relate olfactory response to individual odorous gases, odor measurement using human panels appears to be the method of choice now and for some time to come. Since odor can be caused by hundreds of compounds and is subjective in human response, estimates of national or global odor inventories are meaningless. Odor is also a common source of complaints from people living near AFOs and it is for local impacts that odor has to be quantified. However, there is some confusion in the literature over how to measure odor intensity. Some define an odor unit (OU) as the mass of a mixture of odorants in 1 m3 of air at the odor detection threshold (ODT)—the concentration of the mixture that can be detected by 50 percent of a panel. Others define OU as the factor by which an air sample must be diluted until the odor reaches the ODT. DISTRIBUTION OF EMITTED POLLUTANTS Temporal Scale An atmospheric substance can be characterized by its lifetime (also called residence time) in the atmosphere—defined as the time required to reduce its concentration to 1/e (e is the base of the system of natural logarithms and has a numerical value of about 2.72; 1/e is approximately 0.37) of the initial concentration, with all sources eliminated. The species of interest here span a wide range of lifetimes. Soluble species have lifetimes equivalent to that of water in the atmosphere, about 10 days, depending on precipitation. Reactive

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations species such as NOx and H2S have lifetimes on the order of days or less before they are converted to other more water soluble species such as nitric and sulfuric acids. The lifetimes of VOCs are usually controlled by rates of hydroxyl radical (OH) attack, and range from hours to months. The exception is CH4, with a lifetime of about 8.4 years. N2O is removed by ultraviolet (UV) photolysis and attack by O(1D) (an electronically excited oxygen atom generated by O3 photolysis at wavelengths less than 320 nm) in the stratosphere, and it has a lifetime of about 100 years. N2O is essentially inert in the troposphere. Lifetimes vary with location and time. In the planetary boundary layer (PBL)—that part of the atmosphere interacting directly with the surface of the earth and extending to about 2 km—lifetimes tend to be short; below a temperature inversion, dry deposition can rapidly remove reactive species like NH3. Table 1-3 summarizes typical lifetimes in the PBL for species of interest in this report. Above the PBL, in the free troposphere where wind speeds are higher, temperatures lower, and precipitation less frequent, the lifetime and range of a pollutant may be much greater. Convection transports short-lived chemicals from the PBL to the free troposphere, where they are diluted by turbulent mixing and diffusion. For key atmospheric species involved in nonlinear processes, such as NO and cloud condensation nuclei (CCN), convection can transform local air pollution problems into regional or global atmospheric chemistry problems. TABLE 1-3. Typical Lifetimes in the Planetary Boundary Layer for Pollutants Emitted from Animal Feeding Operations Species Lifetime NH3 ~1-10 day NOx ~1 day H2S ~1 day N2O 100 yr CH4 8.4 yr PM 1-10 days, depending on particle size and composition VOCs hours to months, depending on compound Odora aOdor, which is based on olfactory response to a mixture of compounds, decreases with time in response to dispersion (dilution), deposition, and chemical reactions.

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The Scientific Basis for Estimating Air Emissions from Animal Feeding Operations Spatial Scale Atmospheric concentrations depend on emission or formation rates, loss rates, and mixing, which in turn depend on atmospheric conditions and local geography. Local pollution episodes generally occur with low horizontal wind speeds, as is often the case when a high-pressure ridge dominates the synoptic-scale weather. Inhibited vertical mixing also contributes to high surface concentrations. A strong temperature inversion (temperature increasing rapidly with elevation) at low altitude leads to a shallow PBL and prevents transport of pollutants to the free troposphere. Local concentrations are generally highest when ground-level inversions are strongest. A variety of processes, including subsidence, radiation, and advection, can cause inversions. A detailed discussion is beyond the scope of this report. Local orographic conditions, such as lying in a valley, can exacerbate inversions. Long-lived chemicals such as CH4 and N2O can have large-scale (global) effects, but their local concentrations are not usually a problem. The complexities of the various kinds of air emissions and the temporal and spatial scales of their distribution make their direct measurement at the individual AFO level impractical other than in a research setting. Relatively straightforward methods for measuring emission rates by measuring airflow rates and the concentrations of emitted substances are often not available. Flow rates and pollutant concentrations may be available for some types of confined animal housing but usually not for emissions from soils.