conditions, of course, are an important factor. Estimates of emission rates generated in one type of AFO may not translate readily into others.

EPA has a variety of needs for accurate estimation of air emissions from AFOs. Increasing pressure has been placed on the agency to address these emissions through the Clean Air Act and other federal regulations, and EPA has indicated the need to do so in the future. Also pressing, EPA is under court order to establish new water quality rules by December 2002. The current study will focus on ways to estimate these emissions prior to December 2002 to additionally help assure that rules aimed at improving water quality do not have negative impacts on air emissions.

This interim report is intended to provide findings to date on a series of specific questions from EPA regarding the following general issues: identifying the scientific criteria needed to ensure that estimates of air emission rates are accurate, the basis for these criteria in the scientific literature, and the uncertainties associated with them. It also includes an assessment of the emission estimating approaches in a recent report Air Emissions From Animal Feeding Operations (EPA, 2001a). Finally, it identifies economic criteria needed to assess emission mitigation techniques and best management practices. 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?