If the draft models are implemented with no revisions, farm-level usage will be difficult for U.S. egg farmers.
The Egg Industry Center (EIC) compiled a team of scientists to subject the August 2021 Environmental Protection Agency (EPA) draft air emissions models to a series of “stress tests.” This process was used to gauge how model inputs would impact estimated annual emission factors at 12 different locations nationwide.
The EPA draft models were developed with data from the National Air Emissions Monitoring Study (NAEMS) conducted nearly 15 years ago. Since that time, the U.S. egg industry has changed to widely adopt manure belt and cage-free housing systems and moved away from high-rise housing. Cage-free facilities are projected to be used for 70% of the total U.S. egg production within the near future; however, today’s systems did not exist at the time of NAEMS. Consequently, the proposed EPA draft models will need updated data and incorporate new management and housing to better represent emissions produced by most operations across the U.S.
Researchers struggled to line up everything within the proposed models to published scientific literature. Some of the “stress tests” showed the draft models could be overly sensitive to average daily temperature and relative humidity. This means the average temperature and relative humidity created regional variation in predicted emissions from the draft models. These variations exceed what is published in the scientific literature making the proposed model estimates difficult to apply in many regions of the U.S. where egg production occurs.
Regarding industry-wide implementation, the EIC report highlights that the models would be challenging to implement. The mathematical skills needed to use the models would be a challenge for the average person. In addition, the EPA draft models require bird inventory as input; however, for bird inventories that differ from those in the NAEMS dataset, egg farmers would need to pay close attention to the outputs and work with external expertise to understand if the models yielded reasonable outputs for their specific circumstances.
The EIC report suggests a simpler approach to modeling emissions by developing emission factors from the underlying dataset, and suggests EPA find a way to account for advances made in industry housing and manure storage since the collection of NAEMS data.
The entire EIC technical report reviewing EPA’s draft models can be found here.