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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 8 Conclusions Estimating air emission rates and concentrations from animal feeding operations (AFOs) to guide regulatory and management programs is complicated. The large number and wide variety of operations, even among those for a single livestock type, limit the usefulness of averages in attributing emissions to specific farms. Differences among farms in management practices, such as manure handling, topography, and climate, add to the complexities. Differences in meteorological conditions over time and space also pose difficulties in estimating air emissions. The U.S. Environmental Protection Agency’s (EPA’s) interest has usually focused on estimates of atmospheric concentrations at the “fence line” of farms with large animal feeding operations. This has led to complications because such concentrations are determined both by the generation of emissions and by their dispersion, which is affected by meteorological conditions. Measuring emissions during constant meteorological conditions as a basis for their estimation at other times and locations is difficult. The committee has addressed this problem and concluded that both the EPA and the U.S. Department of Agriculture (USDA) would be better served by an approach to estimating these emissions that is quite different from that used to date. This approach is termed “process-based” modeling, which the committee expects will largely replace the current “emission factor” approach. The committee’s findings and major recommendations that provide the rationale for the approach are listed below. Recommendations for a short-term research agenda (four to five years) are intended to provide EPA and USDA with scientifically sound information for their decisions within that time frame. For the longer term (20-30 years), a re-
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs search program is proposed that will ultimately lead to greatly decreased emissions to the environment of the constituents of air emissions as well as other losses from AFOs while maintaining a high level of production. Effective and early adoption of the committee’s recommendations will require the commitment of EPA and USDA to a course of action that will result in scientifically credible information for their air quality programs. It will require a willingness to change the direction of some current programs and to support a vigorous, expanded research agenda. The committee believes that the results will be of great value, not only in protecting health and the environment, but in reducing costs, and improving the health and welfare of the animals. SETTING PRIORITIES Air emissions from animal feeding operations are of varying concern at different spatial scales, as shown in Table 8-1 (Finding 2, pp. 4, 71). 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 contri- TABLE 8-1 Committee’s Scientific Evaluation of the Potential Importance of AFO Emissions at Different Spatial Scales Emissions Global, National, Regional Local, Property Line, 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 committee’s informed judgment on known or potential impacts from AFOs. Rank order from high to low importance is major, significant, minor, 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 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 mm, respectively.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs butions of AFO emissions to potential effects and the subsequent implementation of control measures. USDA and EPA should first focus their efforts on measurement and control of those emissions of major concern. Measurement protocols, control strategies and management techniques must be emission and scale specific (Finding 3, pp. 5, 71). RECOMMENDATIONS: For air emissions important on a global or national scale (i.e., ammonia [NH3] and the greenhouse gases, methane [CH4], and nitrous oxide [N2O]), the aim is to control emissions per unit of production (kilogram of food produced) rather than emissions per farm. Where the environmental and health benefits outweigh the costs of mitigation it is important to decrease the aggregate emissions. In some geographic regions, 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 with possible health concerns 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. ESTIMATING AIR EMISSIONS There is a general paucity of credible scientific information on the effects of mitigation technology 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 (Finding 4, pp. 6, 72). 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.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Standardized methodology for odor measurement have not been adopted in the United States (Finding 5, pp. 7, 86). RECOMMENDATIONS: Standardized methodology should be developed in the United States for objective measurement techniques to correspond to subjective human response. A standardized unit of measurement of odor concentration should be adopted in the United States. 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., NH3, CH4, hydrogen sulfide [H2S]), and particulate matter (Finding 7, pp. 8, 96). 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. SYSTEMS APPROACH Much confusion exists about the use of the term “animal unit” because EPA and USDA define animal unit differently (Finding 1, pp. 4, 35). RECOMMENDATION: Both EPA and USDA should agree to define animal in terms of animal live weight rather than any arbitrary definition of animal unit. Estimating air emissions from AFOs by multiplying the number of animal units by existing emission factors is not appropriate for most substances (Finding 8, pp. 9, 101). 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.
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs Use of process-based modeling will help provide scientifically sound estimates of air emissions from AFOs for use in regulatory and management programs (Finding 9, pp. 9, 103). 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. 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). 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 (Finding 10, pp. 10, 114). 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. RESEARCH NEEDS 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 (Finding 6, pp. 7, 95). 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
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs chemical dynamics shape the local and regional distribution of these species. 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 nitric oxide [NO]) should be made in the context of total nitrogen losses (Finding 11, pp. 10, 115). RECOMMENDATION: Control strategies aimed at decreasing emissions of reactive nitrogen compounds (Nr) from total animal production 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. 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, USDA), the states, industry and environmental interests, and the research community, including universities (Finding 12, pp. 11, 153). 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 implementation 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 to decrease their releases into the environment. The overall research
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Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs program should include research to optimize inputs to AFOs, optimize recycling of materials, and significantly decrease releases to the environment. 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 (Finding 13, pp. 12, 154). RECOMMENDATIONS: Short-term research priorities should improve estimates of emissions on individual AFOs including 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 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.
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