Researchers comment on proposed EPA models for predicting broiler operation emissions

Single long barn for broiler chickens surrounded by gravel lanes with feed silos in background
Housing for broiler poultry. Image courtesy of Iowa State University. 

AMES, Iowa — Proposed federal draft models designed to guide emissions forecasting for broiler operations need improvement and clarification, according to an in-depth analysis led by Iowa State University scientists. 

In August, the U.S. Environmental Protection Agency released a set of draft models to estimate daily levels of ammonia, hydrogen sulfide and several types of particulate matter (dust) typically emitted from U.S. broiler operations. The original data stemmed from the National Air Emissions Monitoring Study (NAEMS), which measured emissions to eventually guide Clean Air Act policies for livestock and poultry operations. Once finalized, the EPA emissions models may be used by animal feeding operations to determine whether their emissions trigger air quality reporting requirements.   

The agency developed the proposed models for broiler operations using environmentally focused datasets collected between 2005-2007 at a small number of broiler houses in California and Kentucky. 

“EPA’s models are quite outdated,” said Brett Ramirez, associate professor of agricultural and biosystems engineering at Iowa State, and assistant director of the Egg Industry Center. Ramirez is one of the researchers who evaluated the EPA draft emissions models. “The underlying data set is 15 years old. A lot has changed since then, including the sizes of barns, nutrition, genetics and management practices in facilities.”

“The EPA model development approach is also very complicated,” Ramirez said. “Using the EPA model as it is currently proposed would be beyond the capability of many growers – especially smaller facilities - and might even be less accurate than calculating emissions based on the numbers of birds a facility will house during a specific time period.” 

In addition, the EPA model data comes from only four facilities at three sites in Kentucky and California, neither of which are among states that currently produce the most broilers annually.  “At the time of NAEMS, there were limited resources and a best effort was made, but it means the results don’t adequately represent today’s industry across the U.S.,” Ramirez said.   

Other concerns included:  

  • The models estimated greater impacts from multiple barns, even if they housed the same or smaller number of birds. For example, two houses with 10,000 birds were predicted to have more emissions than a single 20,000 bird house. However, emissions should be relatively constant per bird, assuming the same environmental conditions, according to the researchers.
  • The appropriate range of all input values were not provided in the draft EPA report and thus, it was not possible to adequately extrapolate to larger facilities, which have become more common since 2007. 

Along with Ramirez, the research team assessing the EPA model included Guoming Li, assistant professor of poultry science at the University of Georgia, formerly a postdoc at Iowa State, and the late Richard S. Gates, then director of the Egg Industry Center and Iowa Egg Council Endowed Professor at Iowa State. Researchers at the University of Nebraska-Lincoln and University of Tennessee were also involved. Their evaluation of the draft EPA emissions models was published recently in the Journal of Applied Poultry Research and an interpretive summary was featured by the Poultry Science Association.

“Overall, the current draft EPA models are not likely to realistically estimate emissions from a range of broiler operations,” Ramirez said. “As a result of these problems and others outlined in our evaluation, the panel of scientists encourages those whose businesses could be influenced to review this information and consider responding when EPA opens its comment period.” 

This research was jointly supported by the U.S. Poultry and Egg Association (USPEA) and state and USDA Hatch Act funds allocated to Iowa State University, the University of Georgia and the University of Nebraska-Lincoln.  Any conclusions or opinions expressed are those of the investigators and not of USPEA and USDA. No funds provided by USPEA were or will be used for the purposes of influencing legislation and/or government policy or action.



Brett Ramirez, Agricultural and Biosystems Engineering, 515-294-0468,

Ann Robinson, College of Agriculture and Life Sciences Communications, 515-294-3066,