Executive Summary

Public concerns about the environmental effects and, to a lesser extent, the possible health effects of air emissions from animal feeding operations (AFOs, see Appendix B) have grown with the increasing size and geographic concentration of these operations. This intensification has been driven by the economics of domestic and export markets for meat, poultry, milk, and eggs. Public concerns have also grown as the population, both exurbanites and expanding urban centers, have moved into what had been largely rural farming areas. Objectionable odors from AFOs are a significant concern not only to the new residents in these areas, but also to many long-time residents.

Prompted by legislation, especially the Clean Air Act (CAA), as well as by public concerns, the U.S. Environmental Protection Agency (EPA) has been considering what information is needed to define and support feasible regulation of air emissions from AFOs. At the same time, the U.S. Department of Agriculture (USDA) has been using its authority to aid farmers in mitigating the effects of air emissions with modified agricultural practices. Acting jointly, these two agencies asked the Board on Agriculture and Natural Resources (BANR) to evaluate the scientific information needed to address these issues. A 16-person ad hoc committee was appointed, the Committee on Air Emissions from Animal Feeding Operations, which has been guided by a Statement of Task that was agreed upon by the National Academies and the sponsoring agencies (Appendix A).

The Statement of Task directed the committee to

  • review and evaluate the scientific basis for estimating the emissions to the atmosphere of various specified substances from confined livestock and poultry operations;



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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Executive Summary Public concerns about the environmental effects and, to a lesser extent, the possible health effects of air emissions from animal feeding operations (AFOs, see Appendix B) have grown with the increasing size and geographic concentration of these operations. This intensification has been driven by the economics of domestic and export markets for meat, poultry, milk, and eggs. Public concerns have also grown as the population, both exurbanites and expanding urban centers, have moved into what had been largely rural farming areas. Objectionable odors from AFOs are a significant concern not only to the new residents in these areas, but also to many long-time residents. Prompted by legislation, especially the Clean Air Act (CAA), as well as by public concerns, the U.S. Environmental Protection Agency (EPA) has been considering what information is needed to define and support feasible regulation of air emissions from AFOs. At the same time, the U.S. Department of Agriculture (USDA) has been using its authority to aid farmers in mitigating the effects of air emissions with modified agricultural practices. Acting jointly, these two agencies asked the Board on Agriculture and Natural Resources (BANR) to evaluate the scientific information needed to address these issues. A 16-person ad hoc committee was appointed, the Committee on Air Emissions from Animal Feeding Operations, which has been guided by a Statement of Task that was agreed upon by the National Academies and the sponsoring agencies (Appendix A). The Statement of Task directed the committee to review and evaluate the scientific basis for estimating the emissions to the atmosphere of various specified substances from confined livestock and poultry operations;

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs review the characteristics of the agricultural animal industries, methods for measuring and estimating air emissions, and potential best management practices for mitigating emissions; evaluate confined animal feeding production systems in terms of biologic systems; and identify critical short- and long-term research needs and recommend methodologic and modeling approaches for estimating and measuring air emissions and potential mitigation technologies. Making scientifically credible estimates of air emissions from AFOs is complicated by various factors that affect the amounts and dispersion of emissions in the atmosphere. Such factors include the kinds and numbers of animals involved, their diets and housing, the management of their manure (feces and urine, which may also include litter or bedding materials), topography, climatic and weather conditions, and actions taken to mitigate the emissions and their effects. Estimates of emissions generated for one set of conditions or for one type of AFO may not translate readily to others. Accurate estimation of air emissions from AFOs is needed to gauge their possible adverse impacts and the subsequent implementation of control measures. For example, increasing pressure is being placed on EPA to address these emissions through the Clean Air Act and other federal laws and regulations. EPA is under court order to establish new water quality rules for AFOs by December 2002. The need to understand the relationship between actions to mitigate the effects of manure management on water quality and its related effects on air quality prompted EPA to ask for an interim report several months in advance of this final report. The committee’s findings in the interim report (Box ES-1) are encompassed and extended by the findings and recommendations in this report. The contents, including the findings and recommendations, of this report represent the consensus views of the committee and have been formally reviewed in accordance with National Research Council procedures. In addressing its Statement of Task, the committee has come to consensus on 13 major findings, each accompanied by one or more related recommendations. The basis of these findings is discussed more extensively in the body of the report. FINDINGS AND RECOMMENDATIONS Animal Units EPA defines animal units differently than USDA. An EPA animal unit is equal to 1.0 slaughter and feeder cattle, 0.7 mature dairy cows, 2.5 pigs weighing more than 55 pounds, 10 sheep or lambs, and 0.5 horses. USDA defines animal unit as 454 kg (1000 pounds) of animal live weight regardless of species. A consistent basis for defining animal unit will decrease confusion that may exist be-

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs BOX ES-1 Findings from the Interim Report (NRC, 2002a) Finding 1. Proposed EPA regulations aimed at improving water quality may affect rates and distribution of air emissions from animal feeding operations. 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. 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. 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. 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. Finding 6. The model farm construct as described by EPA (2001a) cannot be supported because of weaknesses in the data needed to implement it. 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. 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). SOURCE: NRC (2002a).

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs cause of the differing definitions. The process-based model described in this report is better suited for using a continuous variable (e.g., 500-kg live weight) than a discrete variable (e.g., 1 dairy cow). FINDING 1. Much confusion exists about the use of the term “animal unit” because EPA and USDA define animal unit differently. RECOMMENDATION: Both EPA and USDA should agree to define animal unit in terms of animal live weight rather than an arbitrary definition of animal unit. Spatial Distribution of Effects The various substances that together make up the total air emissions from animal feeding operations differ in quantity, the potential severity of their effects, and the spatial distribution of these effects. Ammonia, whose environmental impacts are reasonably well understood, has relevant impacts that have to be addressed at regional, national, and global scales. On the other hand, odor, whose composition is not well known in scientific terms and whose impacts on the public are difficult to judge, is important mainly at a very local level. Table ES-1, which supports and elaborates Finding 2 below, represents the reasoned judgment of the committee on the relative importance of each substance at the relevant spatial scales strictly for emissions from AFOs. For example, volatile organic compounds (VOCs) play an important role in tropospheric ozone formation, yet such emissions from AFOs are likely to be insignificant compared to other sources in most areas. FINDING 2. Air emissions from animal feeding operations are of varying concern at different spatial scales, as shown in Table ES-1. RECOMMENDATION: These differing effects, concentrations, and spatial distributions lead to a logical plan of action for establishing research priorities to provide detailed scientific information on the contributions of AFO emissions to potential effects and the subsequent implementation of control measures. USDA and EPA should first focus their efforts on the measurement and control of those emissions of major concern. Measurement Protocols and Control Technologies Achieving the overall goal of decreasing the adverse impacts of air emissions from AFOs will require attention to the differences in the character of the various emissions (e.g., their persistence in the atmosphere), in the way they are dis-

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs TABLE ES-1 Committee’s Scientific Evaluation of the Potential Importancea of AFO Emissions at Different Spatial Scales Emissions Global, National, and Regional Local—Property Line or Nearest Dwelling Primary Effects of Concern NH3 Majora Minor Atmospheric deposition, haze N2O Significant Insignificant Global climate change NOx Significant Minor Haze, atmospheric deposition, smog CH4 Significant Insignificant Global climate change VOCsb Insignificant Minor Quality of human life H2S Insignificant Significant Quality of human life PM10c Insignificant Significant Haze PM2.5c Insignificant Significant Health, haze Odor Insignificant Major Quality of human life aRelative importance of emissions from AFOs at spatial scales based on committees’ informed judgment on known or potential impacts from AFOs. Rank order from high to low importance is major, significant, minor, and insignificant. While AFOs may not play an important role for some of these, emissions from other sources alone or in aggregate may have different rankings. For example VOCs and NOx play important roles in the formation of tropospheric ozone; however, the role of AFOs is likely to be insignificant compared to other sources. bVolatile organic compounds. cParticulate matter. PM10 and PM2.5 include particles with aerodynamic equivalent diameters up to 10 and 2.5 μm, respectively. persed, in their environmental effects, and in the effectiveness of various control and management strategies. As noted above, it will also require attention to priorities based on the geographic scale at which impacts are of greatest concern. The local scale is considered the AFO boundary or nearest occupied dwelling. The regional scale may be as small as a single topographic land feature (e.g., a stream valley) or as large as a multistate airshed. FINDING 3. Measurement protocols, control strategies, and management techniques must be emission and scale specific. RECOMMENDATIONS: For air emissions important on a global or national scale (i.e., ammonia and the greenhouse gases methane [CH4] and nitrous oxide [N2O]), the aim is to control emissions per unit of production (kilograms of food produced) rather than emissions per farm. Where the environmental and health benefits outweigh the costs of mitigation it is important to decrease aggregate emissions. In some geographic regions,

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs aggregate emission goals may limit the number of animals produced in those regions. For air emissions important on a local scale (hydrogen sulfide [H2S], particulate matter [PM], and odor), the aim is to control ambient concentrations at the farm boundary and/or nearest occupied dwelling. Standards applicable to the farm boundary and/or nearest occupied dwelling must be developed. Monitoring should be conducted to measure concentrations of air pollutants of possible health concern at times when they are likely to be highest and in places where the densities of animals and humans, and typical meteorological conditions, are likely to result in the highest degree of human exposure. Current Best Management Plans As noted in the committee’s interim report, available estimates of emission factors, rates, and concentrations are sufficiently uncertain that they provide a poor basis for regulating or managing air emissions from AFOs. Nevertheless, some best management practices to mitigate the adverse effects of air emissions appear at face value to warrant their use, even as new information on mitigation and best management practices is being developed. Although the committee favors a strong focus on research to develop needed new information, the use of clearly effective measures should be encouraged while new information is being developed. FINDING 4. There is a general paucity of credible scientific information on the effects of mitigation technologies on concentrations, rates, and fates of air emissions from AFOs. However, the implementation of technically and economically feasible management practices (e.g., manure incorporation into soil) designed to decrease emissions should not be delayed. RECOMMENDATION: Best management practices (BMPs) aimed at mitigating AFO air emissions should continue to be improved and applied as new information is developed on the character, amount, and dispersion of these air emissions, and on their health and environmental effects. A systems analysis should include impacts of a BMP on other parts of the entire system. Odors Odors associated with AFO emissions are often regulated in response to nuisance complaints rather than demonstrated health effects. The measurement of

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs odor concentrations downwind from AFOs is based on olfactometers that relate odor strength to a standard (usually n-butanol) or uses the judgment of panels of experts trained to distinguish odor strengths. While standardized terminology and measures have been developed in Europe, a similar effort has not yet occurred in the scientific community in the United States. Odors continue to be a problem with AFOs at the local level. Continuing research into the constituents of odor with a goal of providing a basis for scientific agreement for standards is needed. FINDING 5. Standardized methodologies for odor measurement have not been adopted in the United States. RECOMMENDATIONS: Standardized methodology should be developed in the United States for objective measurement techniques of odors to correspond to subjective human response. A standardized unit of measurement of odor concentration should be adopted in the United States. Dispersion Modeling FINDING 6. The complexities of various kinds of air emissions and the temporal and spatial scales of their distribution make direct measurement at the individual farm level impractical other than in a research setting. Research into the application of advanced three-dimensional modeling techniques accounting for transport over complex terrain under thermodynamically stable and unstable planetary boundary layer (PBL) conditions offers good possibilities for improving emissions estimates from AFOs. RECOMMENDATION: EPA should develop and carry out one or more intensive field campaigns to evaluate the extent to which ambient atmospheric concentrations of the various species of interest are consistent with estimated emissions and to understand how transport and chemical dynamics shape the local and regional distribution of these species. Measurement Protocols Accurate measurement of air emissions is dependent on the availability and use of protocols that are both technically sound and practical for use in the field, as well as the laboratory. Such measurement protocols are available for measur-

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs ing nitrous oxide and nitric oxide (NO). Improved measurement protocols are needed for other substances. Particulate matter, odor, and volatile organic compounds are important emissions at the local level, but pose some special problems because their constituents and emission rates vary widely among AFOs and their locations. FINDING 7. Scientifically sound and practical protocols for measuring air concentrations, emission rates, and fates are needed for the various elements (nitrogen, carbon, sulfur), compounds (e.g., ammonia [NH3], CH4, H2S), and particulate matter. RECOMMENDATIONS: Reliable and accurate calibration standards should be developed, particularly for ammonia. Standardized sampling and compositional analysis techniques should be provided for PM, odor, and their individual components. The accuracy and precision of analytical techniques for ammonia and odor should be determined, including intercomparisons on controlled (i.e., synthetic) and ambient air. Emission Factors The “emission factor” approach for estimating air emissions is based on measuring emissions from a set of defined AFOs to obtain an “average” emission per unit (e.g., per animal unit or per unit of production). These emission factors can then be used to estimate emissions for other AFOs by multiplying the emission factor by the number of observed units to which the average applies. As noted in the committee’s interim report, the existing emission factors for AFOs are generally inadequate because of the limited number of measurements on which they are based, as well as the limited generality of the models for which the emission factors have been developed (see Appendix L). Improving existing emission factors to the point where they could provide scientifically credible estimates of either emission rates or concentrations would require major efforts in getting sufficient observations to characterize the variability among and within AFOs. The committee (in Finding 9 and Chapter 5) suggests that an alternative approach for estimating emissions, a process-based modeling approach, can provide more useful estimates for most of the air emission substances of concern. Particulate matter is the main exception and may require additional efforts to improve emission factors. Allocation of overall resources for improving and evaluating emission estimates should focus on the committee’s recommended process-based modeling approach for all emissions mentioned, except for particulate matter.

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs FINDING 8. Estimating air emissions from AFOs by multiplying the number of animal units by existing emission factors is not appropriate for most substances. RECOMMENDATION: The science for estimating air emissions from individual AFOs should be strengthened to provide a broadly recognized and acceptable basis for regulations and management programs aimed at mitigating the effects of air emissions. Process-Based Model To counter the tendency to consider only on-farm inputs and outputs from AFOs, to ensure more accurate accounting of the flows of chemicals and other air emission substances from the operation, and to provide a “mass balance” control for the total flow of inputs to and outputs from the operation, the committee recommends a “process-based modeling” approach for estimating air emissions. The process-based modeling approach can be used to estimate the flows of elements (nitrogen, sulfur, carbon) and of compounds containing these elements. The committee believes, with some reservations, that this approach might be used for estimating odor emissions. The only substance of direct concern to the committee for which this approach may not be well suited is particulate matter. This approach involves the specification of mathematical models that describe the movement of various substances of interest at each major stage of the process of producing livestock products: movement into the next stage, movement in various forms to the environment, and ultimately movement into products used by humans. Mass balance constraints serve as a check on the whole system to ensure that estimates of movements of substances out of the system do not exceed the amounts available within the system. FINDING 9. Use of process-based modeling will help provide scientifically sound estimates of air emissions from AFOs for use in regulatory and management programs. RECOMMENDATIONS: EPA and USDA should use process-based mathematical models with mass balance constraints for nitrogen-containing compounds, methane, and hydrogen sulfide to identify, estimate, and guide management changes that decrease emissions for regulatory and management programs. EPA and USDA should investigate the potential use of a process-based model to estimate mass emissions of odorous compounds and potential management strategies to decrease their impacts.

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs EPA and USDA should commit resources and adapt current or adopt new programs to fill identified gaps in research to improve mathematical process-based models to increase the accuracy and simplicity of measuring and predicting emissions from AFOs (see short-term and long-term research recommendations). Systems Analysis The emission factor approaches in current use focus on the “on-farm” inputs to and outputs from an AFO. This ignores the potential environmental effects associated with “off-farm” production of feed and other materials used in an AFO. Since some of the feed for typical AFOs is imported from other farms, and a portion of the manure is often exported from the AFO for use on other farms (some regional and species differences exist), restricting consideration of inputs and outputs to a single AFO may not completely represent the full environmental effects of the operation. A “systems approach” that considers both the on-farm and the off-farm inputs and outputs would provide a more accurate description of overall impacts. FINDING 10. A systems approach, which integrates animal and crop production systems both on and off (imported feeds and exported manure) the AFO, is necessary to evaluate air emissions from the total animal production system. RECOMMENDATION: Regulatory and management programs to decrease air emissions should be integrated with other environmental (e.g., water quality) and economic considerations to optimize public benefits. Nitrogen Emissions Because of its potential environmental impacts at regional, national, and global scales, instituting control strategies for nitrogen emissions should be assigned high priority. Sufficient information is currently available to do this at all geographic scales. FINDING 11. Nitrogen emissions from AFOs and total animal production systems are substantial and can be quantified and documented on an annual basis. Measurements and estimates of individual nitrogen species components (i.e., NH3, molecular nitrogen [N2], N2O, and NO) should be made in the context of total nitrogen losses. RECOMMENDATION: Control strategies aimed at decreasing emissions of reactive nitrogen compounds (Nr) from total animal production

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs systems should be designed and implemented now. These strategies can include both performance standards based on individual farm calculations of nitrogen balance and technology standards to decrease total system emissions of reactive nitrogen compounds by quantifiable amounts. Research The two major federal agencies with regulatory or management responsibilities relative to air emissions from AFOs are EPA and USDA. Each of these agencies also has research responsibilities in support of its action programs—responsibilities that are typically serviced through “in-house” research staffs. Close cooperation is needed between the two agencies in setting and supporting research priorities relative to air emissions. Inputs and participation from the full range of state, private, and research institutions with relevant interests are needed to ensure that concerns about air emissions are addressed with the full complement of needed expertise. The importance of food production from AFOs, coupled with the potential environmental effects from air emissions, demands substantial research efforts in both the short and the long term. These issues will not be resolved without addressing the appropriate funding of these efforts. Current allocations of funding aimed at AFO air emissions are not adequate or appropriate in view of the amount of concern about these emissions and the recent growth in AFO livestock production. Research in the short term (four to five years) can significantly improve the capability of the process-based modeling approach for estimating air emissions. A long-term (20-30 years) research program that encompasses overall impacts of animal production on the environment, as proposed here, can have even more substantial results in decreasing overall impacts on the environment, while sustaining production at a high level. FINDING 12. USDA and EPA have not devoted the necessary financial or technical resources to estimate air emissions from AFOs and develop mitigation technologies. The scientific knowledge needed to guide regulatory and management actions requires close cooperation between the major federal agencies (EPA and USDA), the states, industry and environmental interests, and the research community, including universities. RECOMMENDATIONS: EPA and USDA should cooperate in forming a continuing research coordinating council (1) to develop a national research agenda on issues related to air emissions from AFOs in the context of animal production systems and (2) to provide continuing oversight on the imple-

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs mentation of this agenda. This council should include representatives of EPA and USDA, the research community, and other relevant interests. It should have authority to advise on research priorities and funding. Exchanges of personnel among the relevant agencies should be promoted to encourage efficient use of personnel, broadened understanding of the issues, and enhanced cooperation among the agencies. For the short term, USDA and EPA should initiate and conduct a coordinated research program designed to produce a scientifically sound basis for measuring and estimating air emissions from AFOs on local, regional, and national scales. For the long term, USDA, EPA, and other relevant organizations should conduct coordinated research to determine which emissions (to water and air) from animal production systems are most harmful to the environment and human health, and to develop technologies that decrease their releases into the environment. The overall research program should include research to optimize inputs to AFOs, optimize recycling of materials, and significantly decrease releases to the environment. The reality of budget constraints in allocating research funds to address problems of air emissions requires a careful weighing of several factors, including those that affect both the implementation costs and the societal benefits. Finding 2 proposes a way of ranking both action and research opportunities among the emission substances based on amounts of concern or impacts and geographic scale of impacts. A more complete listing of factors is needed for setting both short- and long-term research priorities and for allocating research funds. FINDING 13. Setting priorities for both short- and long-term research on estimating air emission rates, concentrations, and dispersion requires weighing the potential severity of adverse impacts, the extent of current scientific knowledge about them, the potential for advancing scientific knowledge, and the potential for developing successful mitigation and control strategies. RECOMMENDATIONS: Short-term research priorities should improve estimates of emissions from individual AFOs including the effects of different control technologies: Priority research for emissions important on a local scale should be conducted on odor, PM, and H2S (also see Finding 2). Priority research for emissions important on regional, national, and

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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs global scales should be conducted on ammonia, N2O, and methane (also see Finding 2). Long-term research priorities should improve understanding of animal production systems and lead to development of new control technologies. SUMMARY These findings and recommendations, taken together, point to two major changes in direction for improving the basic information needed for dealing with the adverse effects of air emissions from AFOs. One is to replace the current emission factor approach for estimating and tracking the rates and fates of air emissions using a process-based modeling approach with mass balance constraints. The second is to initiate a substantial long-term research program on the overall system of producing food from animal feeding operations with the goal of eliminating the release of undesirable air and other emissions into the environment. 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. 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 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.