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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 1 Introduction BASIS FOR THIS REPORT Increases in the size and geographical concentration (see Appendix K) of animal feeding operations (AFOs; see Appendix B) and growing concerns with emissions from them appear to be leading toward regulation or other means to mitigate their air emissions. Recognizing the need for solid scientific information on which to base regulatory or other program decisions, the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Agriculture (USDA) asked the Board on Agriculture and Natural Resources to evaluate the scientific basis for estimating various kinds of air emissions from AFOs. The specific requirements to guide this study were dictated by the committee’s Statement of Task (Appendix A). A 16-person committee was appointed with expertise in various relevant disciplines (see “About the Authors” section) to conduct the study. The policy and program issues connected to air emissions from AFOs are multifaceted. The agencies that sponsored and funded this study (EPA and USDA) have direct and indirect program interests. Under the Clean Air Act (CAA) and the Clean Water Act (CWA), EPA is responsible for defining regulatory programs through the states to improve and maintain the nation’s air and water quality. USDA sponsors programs to provide farmers and other landowners with technical and financial assistance to adopt practices that will improve the environmental quality of land and related air and water resources. Both agencies have research programs aimed at providing scientific information necessary for pursuing their program goals. In addition, lawmakers and those making policy decisions at all levels of government require solid scientific information to carry out their tasks. This report evaluates the availability of this information and proposes ways to acquire it.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs The research programs supported by EPA and USDA are obvious candidates for providing much of the needed information. USDA has by far the largest overall research program of the two agencies. It has in-house capabilities (Agricultural Research Service, Economic Research Service, and National Agricultural Statistics Service) and helps support an extensive extramural research program conducted through state universities and a system of agricultural research stations. Total funding for these programs is about five times that of EPA’s program, which is conducted largely through a system of EPA research labs. Only small parts of these programs, however, are devoted to research related to air emissions. The findings and recommendations in this report are aimed in large part at the leaders and scientists of the EPA and USDA research programs, but they are also aimed at the entire community interested in addressing the issues posed by the adverse effects of air emissions from animal feeding operations. This includes leaders in the scientific research community, agriculture in general, environmental interests, people affected by the emissions, and the farmers who ultimately have to deal directly with their causes. CONCERNS WITH AIR EMISSIONS The EPA and USDA have asked the committee to address the issues relating to the substances shown in Table 1-1. The committee added nitric oxide (NO) because it is produced by AFOs and their associated grain production and manure disposal, and because it can have significant environmental effects. As Table 1-1 indicates, the substances of concern vary in their classifications as air pollutants. They also vary in the severity and scale of their effects. 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 feeding operations. Additionally, particulate matter may blow from farms to nearby residences and trouble residents because of actual or perceived health effects. Equally important are the various substances in air emissions that contribute to environmental degradation, such as eutrophication of water bodies (caused by reactive nitrogen compounds) or climate change (induced by the greenhouse gases methane and nitrous oxide). The committee believes that these concerns warrant serious attention to determine the effects of AFOs and to mitigate their detrimental air emissions. THE INTERIM REPORT As part of its charge, EPA asked that the committee provide an interim report in the spring of 2002 to give it an early indication of findings that would help in planning regulations to decrease impacts of AFOs on water quality. In particular, EPA was concerned that possible actions to improve water quality might have an
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs TABLE 1-1 Substances in AFO Emissions That the Committee Was Tasked to Address and Their Respective Classificationsa Species Criteria Pollutant Hazardous Air Pollutant (HAP) Greenhouse Gas Regulated Air Pollutant NH3b — — — X N2Oc — — X — NOx X — — X CH4 — — X — VOCsd — Xe — Xf H2Sg — — — X PM (TSP)h — — — X PM10 X — — X PM2.5 X — — X Odori — — — X aSee Appendix B for definitions and Chapter 6 for regulations. bAmmonia is not a criteria pollutant but is a precursor for secondary PM2.5, which is a criteria pollutant. cNitrous oxide is not a precursor for the formation of tropospheric ozone, but is a greenhouse gas. It is not considered to be part of NOx (the sum of NO and NO2), which contributes to formation of ozone, a criteria pollutant. dVolatile organic compounds (VOCs), sometimes referred to as reactive organic gases (ROGs), contribute to the formation of ozone, a criteria pollutant. eSome, but not all, VOCs are listed as Hazardous Air Pollutants (HAPs). fSome VOCs are regulated as HAPs, and some are regulated as ozone precursors. gHydrogen sulfide is not listed as a criteria pollutant or a hazardous air pollutant (HAP). However, it is a regulated pollutant because it is listed as having a New Source Performance Standard (NSPS). It may be added to the HAPs list in the near future. h Particulate matter. Prior to 1987, PM was a criteria pollutant and regulated as total suspended particulate (TSP). Currently, the PM fractions listed as criteria pollutants are PM10 and PM2.5. However, TSP emissions are regulated in some states. iOdor is a regulated pollutant in some states. State air pollution regulatory agencies regulate it based on a nuisance standard. adverse impact on air emissions. The committee was also asked to assess the approach for estimating air emissions from AFOs presented in a draft contract report to EPA Emissions from Animal Feeding Operations (EPA, 2001a). The committee’s interim report provided EPA with findings on the following: identification of the scientific criteria needed to ensure that air emission rates are reasonable, the basis for these criteria as documented in the scientific literature, and the uncertainties associated with them. The interim report was reviewed in accordance with National Research Council procedures. It responded directly to a series of questions posed by EPA: What are the scientific criteria needed to ensure that reasonably appropri-
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs ate 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 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)? 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? Responses to those questions are summarized in eight findings along with a brief discussion of each finding in the committee’s interim report (NRC, 2002a; Box 1-1). These interim report findings provide a foundation for the findings and recommendations in this report, which points to the limitations of currently available information on air emissions from AFOs. It also points to the need for new approaches to make such estimates, and describes further research needed to support regulatory and management programs aimed at decreasing air emissions. SCALE AND IMPACT OF EMISSIONS FROM ANIMAL FEEDING OPERATIONS The scope of the issues arising from AFO air emissions is large. A large fraction of the crops grown in the United States are fed to domesticated animals to produce meat, milk, and eggs for human consumption. As animal populations have grown in some locations and become more concentrated on larger farms, and as humans leave urban areas, concern has increased because of possible adverse effects on human health and the environment. Between 1982 and 1997, the number of animal feeding operations in the United States decreased by 51 percent, while livestock production increased 10 percent (Gollehon et al., 2001). In some areas, even greater changes in concentration have occurred (G. Saunders, North Carolina Department of Environment and Natural Resources, personal communication, 2002). As AFOs have increased in size and geographical concentration (see Appendix K), the potential health and
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs BOX 1-1 Findings and Discussion from the Interim Report Finding 1. Proposed EPA regulations aimed at improving water quality may affect rates and distributions of air emissions from animal feeding operations. Discussion: Regulations aimed at protecting water quality would probably affect manure management at the farm level, especially since they might affect the use of lagoons and the application of manure on cropland or forests. For example, the proposed water regulations may mandate nitrogen (N) or phosphorus (P) 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 will 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 nitrogen requirement for crop production. These practices may increase nitrogen volatilization to the air. The committee was not informed of specific regulatory actions being considered by EPA (beyond those addressed in the Federal Register) to meet its December 2002 deadline for proposing regulations under the Clean Water Act. 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. Discussion: Management practices (e.g., feeding, manure management, crop management) vary widely among individual farms. Estimates of emissions based on regional or other averages are unlikely to capture significant differences among farms that will be relevant for guiding emissions management practices aimed at decreasing their effects. Information on the spatial relationships among individual farms and the dispersion of air emissions from them is needed. Furthermore, developing methods to estimate emissions at the individual farm level was the stated objective of EPA’s recent study (EPA, 2001a). 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.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Discussion: Although it is possible in a carefully designed research project to measure concentrations and airflows (e.g., building ventilation rates) to estimate air emissions and attribute them to individual AFOs, it is not practical to conduct such projects for more than a small fraction of AFOs. Direct measurements for sample farms will be needed in research programs designed to develop estimates of air emissions applicable to various situations. 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. Discussion: The components or factors used to characterize feeding operations are chosen for their usefulness in explaining dependent variables, such as the mass of air emissions per unit of time. The emission factor method, which is based on the average amount of an emitted substance per unit of activity per year (e.g., metric tons of ammonia per thousand head of cattle per year), can be useful in estimating annual regional emissions inventories for some pollutants, provided that sufficient data of adequate quality are available for estimating the relationships. Finding 5. Reasonably accurate estimates of air emissions from AFOs at the individual farm level require defined relationships between air emissions and various factors. Depending on the character of the AFOs in question, these factors may include animal types, nutrient inputs, manure handling practices, output of animal products, management of feeding operations, confinement conditions, physical characteristics of the site, and climate and weather conditions. Discussion: The choice of independent variables used to make estimates of air emissions from AFOs will depend on the ability of the variables to account for variations in the estimates and on the degree of accuracy desired, based on valid measurements at the farm level. Past research indicates that some combination of the indicated variables is likely to be important for estimates of air emissions for the kinds of operations considered in this report. The specific choices will depend on the strength of the relationships for each kind of emission and each set of independent variables. Finding 6. The model farm construct as described by EPA (2001a) cannot be supported because of weaknesses in the data needed to implement it.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Discussion: Of the nearly 500 possible literature sources for estimating emissions factors identified for EPA (2001a), only 33 were found by the report’s authors to be suitable for use in the model farm construct. The committee judged them to be insufficient for the intended use. The breadth in terms of kinds of animals, management practices, and geography in this model farm construct suggests that finding adequate information to define emission factors is unlikely to be fruitful at this time. Finding 7. The model farm construct used by EPA (2001a) cannot be supported for estimating either the annual amounts or the temporal distributions of air emissions on an individual farm, subregional, or regional basis because the way in which it characterizes feeding operations is inadequate. Discussion: Variations in many factors that could affect the annual amounts and temporal patterns of emissions from an individual AFO are not adequately considered by the EPA (2001a) model farm construct. The potential influences of geographic (e.g., topography and land use) and climatic differences, daily and seasonal weather cycles, animal life stages, management approaches (including manure management practices and feeding regimes), and differences in state regulations are not adequately considered. Furthermore, aggregating emissions from individual AFOs using the EPA (2001a; not a stated objective) model farm construct for subregional or regional estimates cannot be supported for similar reasons. However, with the appropriate data identified there may be viable alternatives to the currently proposed approach. Finding 8. A process-based model farm approach that incorporates “mass balance” constraints for some of the emitted substances of concern, in conjunction with estimated emission factors for other substances, may be a useful alternative to the model farm construct defined by EPA (2001a). Discussion: The mass balance approach, like EPA’s model farm approach, starts with defining feeding operations in terms of major stages or activities. However, it focuses on those activities that determine the movement of nutrients and other substances into, through, and out of the system. Experimental data and mathematical modeling are used to simulate the system and the movement of reactants and products through each component of the farm enterprise. In this approach, emissions of elements (such as nitrogen) cannot exceed their flows into the system. SOURCE: NRC (2002a).
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs environmental effects of their emissions to water and air have been of increasing concern, especially to those who live nearby. Concerns include potential health impacts of water and air pollution, disagreeable odors, and the possibility of catastrophic events related to extreme weather events. In addition to local and regional effects, animal operations add significantly to the global burden of greenhouse gases, particularly methane and nitrous oxide, which contribute to global climate change (IPCC, 2001). Ammonia in the air contributes to the formation of fine particulate matter over large regions, and its deposition contributes to eutrophication of coastal bays and estuaries. To understand the historical trends, it is useful to consider the growth that has occurred in the populations of both humans and animals in some locations, made possible by the industrial fixation of nitrogen on a large scale, especially the production of fertilizer by the Haber-Bosch process (the reaction of molecular nitrogen [N2] with hydrogen [H2] to make ammonia, which is then used to make other reactive nitrogen [Nr] compounds; see Appendix B). The use of inorganic fertilizers (particularly ammonium nitrate and urea) has greatly increased the production of agricultural crops, especially since 1950, and made possible the rapid increases in the populations of both humans and domesticated animals that have taken place in the twentieth century (Smil, 2001). Nitrogen flows in U.S. agriculture, including crops and animal production, are shown for base year 1997 in Figure 1-1. (Note that the figure does not include the NOx generated from the combustion of fuel used to produce and transport crops or to transport animal waste or animal products from farms.) About 18.5 Tg FIGURE 1-1 Mass flows (teragrams of nitrogen per year) of new reactive nitrogen in U.S. agriculture in 1997. Adapted from Howarth et al., 2002.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs N/yr (1 Tg = 1012 g or 1 million metric tonnes) of new Nr is added to cropland in the form of inorganic fertilizer (11.2 Tg N/yr), cultivation-induced biological nitrogen fixation (5.9 Tg N/yr), and atmospheric deposition of NOy (1.2 Tg N/yr). Of this, 10.5 Tg N/yr is harvested in crops and 8.0 Tg N/yr is lost from cropland to water and air (some as N2). Of the 10.5 Tg N/yr in harvested crops, 5.9 Tg N/ yr is fed to animals, 1.3 is fed to people, 2.1 is exported, and the remaining 1.2 is lost to the environment (including some N2). Of the 5.9 Tg N/yr fed to animals, 5.0 Tg N/yr is lost to the environment and the remaining 0.9 is fed to people in the United States. Thus, of the 18.5 Tg N/yr added to cropland from new sources (not including N recycled in manure), humans in the United States consume 2.2 Tg N/ yr (all of which is lost to the environment). In fulfilling their responsibilities to protect human health and the environment, EPA and state and local environmental agencies are grappling with the issues of how to quantify the size and scope of AFO emissions and how to decrease their adverse effects in an economical way based on the best science available. Addressing these adverse effects has implications not only for direct effects on human health and the environment, but also for indirect effects on the structure of the U.S. agricultural economy. The problems caused by animal feeding operations have occurred in part because of the concentration of production in large operations, which is driven by market economics. Actions to decrease the adverse effects (potential economic and social consequences) could lead to the further concentration of production or, alternatively, to a reversal of that trend. Users of this report should be cognizant of these possibilities. POLICY CONTEXT Two federal agencies, EPA and USDA, have programs that address the effects of emissions from AFOs. These programs are discussed in detail in Chapter 6. Implementation of programs by both agencies is aided by the states. EPA’s programs rely on regulation, while USDA’s rely on management, mainly by farmers’ actions. The two approaches have the potential to be complementary rather than conflicting if there is close coordination among EPA, USDA, and state governments. Regulations and programs aimed at mitigating air emissions from AFOs are effective and publicly acceptable only if the information on which they are based is defensible. Public trust can be eroded if regulations and programs appear to be based on poor information. As noted in the committee’s interim report, the approach for estimating emissions proposed for use by EPA (2001a) is not adequate because of data limitations and the way in which it characterizes individual farms in relation to emissions (NRC, 2002a). Although current information is not sufficient in many cases to support defensible regulations, EPA is under pressure to take actions to decrease air emissions from AFOs. As a result, the committee believes that EPA must develop new information in a timely manner.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs While EPA must rely on quantitative estimates of air emission rates and concentrations of pollutants in the ambient air for regulating air emissions, USDA programs to date have relied less on quantitative estimates of emissions and more on the expected favorable effects of best management practices (BMPs). The committee believes that better understanding of the measurable effects of these practices would help guide USDA in mitigating air emissions and their adverse effects. Thus, both of the federal agencies face much the same issue—a lack of solid scientific information for pursuing their tasks. SCIENCE CONTEXT Sound understanding of AFO air emissions and their effects requires the expertise of numerous scientific disciplines, including animal nutrition and metabolism, farm practices, atmospheric chemistry, meteorology, air monitoring, statistics, and epidemiology and toxicology (for health effects). Developing this understanding will also require input from agricultural engineering and economics, and related disciplines. To assemble, integrate, and interpret this broad array of information is a formidable task, especially in view of the different animal types and geographical and climate conditions in which AFOs are found. EPA has a variety of needs for more accurate estimates of air emissions from AFOs, including the following: general monitoring of the nation’s air quality; determining what pollutants are in the nation’s ambient air, their concentrations and their sources; identifying the emissions that may have the greatest adverse effects on human health or the environment; improving regulatory approaches; and assessing the effectiveness of various abatement technologies and strategies. USDA has a broadly similar need for accurate information, but one that focuses more directly on the kinds of management actions that farmers can take to mitigate emissions at the farm level. Despite numerous reports in the literature, little of the information and analysis now available was designed to meet these needs. There is no comprehensive, sound, science-based set of data on emissions from AFOs. Perhaps the most serious problem in generating such a database is the great variability in AFO emission rates, which cannot be addressed solely by developing more accurate measuring instruments. Emission rates can vary ten-fold or more during periods as short as an hour or as long as a year—with changes in the management of the animals, their feed, and weather conditions. Improved accuracy in what is recorded at one location and time may matter very little (Arogo et al., 2001; Mount et al., 2002). This problem can be resolved only by
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs devising a regulatory and management strategy that recognizes and accommodates this variability, combined with a measurement plan that collects sufficient information to address concerns and direct future efforts. This approach will vary with the substance and with the concern. For example, potential effects on human health will generally be inferred from short-term (e.g., hourly or daily) local concentrations (and compositions in the case of particulate matter), whereas effects on climate change will be inferred from regional or national annual emission inventories. In an ideal world, the data would be accurate and precise, broad in coverage of both substances and AFO types and operations, based on sound sampling plans, timely, detailed (addressing geography, time intervals, climatic conditions, etc.), well documented, in a readily accessible form, and inexpensive. Meeting all of these desirable features will undoubtedly lead to conflicts, so compromises must be made. CHALLENGES Facing the need for defensible information on air emissions from AFOs in a timely manner is a major challenge for EPA and USDA. Neither has yet addressed the need for this information in defining high-priority research programs. Neither has asked for nor secured the level of funding required to provide the necessary information. Each has pursued its regulatory and farm management programs under the assumption that the best currently available information can be used to implement its program goals. The committee believes that the scope and complexity of the information needed by these agencies, as well as the potential environmental impacts of air emissions from AFOs, require a concentrated, focused, and well-funded research effort. Such an effort is described in this report. STRUCTURE OF THE FINAL REPORT Chapter 2 describes in broad terms the economics and operating practices of the animal feeding industry and its major sectors (dairy, beef cattle, swine, and poultry). This chapter, along with Chapter 6 on government regulations and programs, sets the stage for the other chapters, which address more directly air emissions and the scientific bases for estimating their rates, concentration, and distribution. Chapter 3 describes the kinds of air emissions produced by animal feeding operations and their potential impacts on the environment and human health. Chapter 4 examines the state of the science for measuring air emissions, including measurement principles and techniques suited to various on- and off-farm situations. Chapter 5 describes approaches for estimating air emissions from AFOs, including an evaluation of a process-based (mass balance) approach for
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs estimating emissions for each component of the overall production process. In this approach, the origin and ultimate destination of each major chemical element (nitrogen, carbon, sulfur and phosphorus) in the animals’ feed is modeled. This chapter also compares the mass balance approach with other approaches for estimating emissions at the individual farm level, within regulatory and management contexts. Chapter 6 describes the legal and programmatic structure for managing—by public oversight and mitigation—air emissions from AFOs. The information in Chapters 1-6 then serves as the basis for defining both short-term (4-5 years) and long-term (20-30 years) research programs in Chapter 7. The short-term program is designed to provide defensible estimates of air emissions that could be used to support responsible regulation. The long-term program views the animal feeding system more broadly in order to decrease AFO inputs, increase recycling of manure, and eliminate or greatly decrease adverse effects on health and ecosystems. Both the short-term and the long-term research programs are ambitious and will require cooperation and participation by the full range of the research community. Finally, Chapter 8 summarizes the committee’s major conclusions and recommendations.
Representative terms from entire chapter: