Evaluating draft Environmental Protection Agency emissions models for broiler operations

In August 2021, the U.S. Environmental Protection Agency (EPA) released draft models to estimate daily NH3, H2S, PM2.5, PM10, and total suspended particulates emissions from U.S. broiler operations using inputs of daily mean ambient temperature, relative humidity, and live animal weight. The EPA developed these models using datasets collected between 2005 and 2007. It is important to note that over 15 yr have passed since the original data were collected, and broiler genetics, nutrition, and management have improved considerably. These models, if adopted, could have substantial impact on the U.S. broiler industry regarding air emission management and regulation. The objectives of this work were to 1) evaluate the draft EPA emissions model robustness and practicality, and 2) assess the estimated annual emissions for broiler operations in representative U.S. climates using the draft EPA models. The draft EPA emissions models and coefficients were coded and checked against example calculations provided in the draft EPA report, with discrepancies noted. The draft EPA models with log transforms were found to be overly complicated for deployment by most laypersons intending to estimate daily annual emissions from a house or a site with multiple houses. Substantive, fundamental model challenges were uncovered due to narrow model input ranges. For example, lower bird inventory (<20,000 birds per house) generally resulted in much greater emission factors per bird, but should be relatively constant for different inventories at the same environmental conditions; all particulate matter models predicted negative emissions at lower bird inventories; and of the 5 air pollutant models presented, only ammonia was found to be potentially limiting for larger farms in terms of exceeding the threshold of 100 tons per yr. We conclude that the current draft EPA emissions models are not appropriate for accurately or reasonably estimating emissions for a realistic range of broiler operations in their current forms. Revisions are suggested to accommodate the range of climates encountered within the U.S. broiler industry and to better reflect relations found in the scientific literature.