Gaseous emissions from livestock production continue to receive increasing attention due to concerns over their environmental and health impacts. Local concerns over gaseous emissions are usually focused on odor and environmental impacts. For example, ammonia (NH3) is usually of concern for its potential negative impacts on local environments or ecological systems due to deposition, whereas greenhouse gases (GHGs) emissions are of concern for their potential impacts on global climate change. However, it is important to understand the quantity and composition of gasses being emitted to the atmosphere. The primary GHGs associated with livestock production are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Information on GHG emissions from U.S. swine production facilities is meager, especially under commercial production conditions.
Therefore, the objective of this study was to quantify the emissions of GHGs and ammonia from a Midwestern production-scale breeding/gestation/farrowing facility over a one-year period. This study will begin to establish the baseline GHG emissions and contribute to national emissions inventory on ammonia emissions for swine production in the United States, particularly under Midwestern production conditions.
A 4300 sow capacity breeding/gestation/farrowing facility in central Iowa was used in this one-year intensive monitoring study. The facility consisted of one breeding/early gestation barn, one late gestation barn, and two farrowing buildings with 9 farrowing rooms each (40 farrowing crates per room). The farrowing rooms held manure in a shallow pit that was drained into an external storage at the end of each farrowing cycle (~21days). The breeding/early gestation barn and late gestation barn held manure in a deep pit of each barn. Manure from the barns and the external storage was pumped out twice a year.
A Mobile Air Emissions Monitoring Unit (MAEMU) was used to continuously measure variables needed to determine the gaseous emissions from the breeding/gestation barns and two farrowing rooms. For each monitored barn/room the following data were collected on a 30 second basis: fan running status, building static pressure, indoor air temperature and relative humidity (RH), outdoor air temperature and RH, and barometric pressure. Gaseous concentrations of the exhaust air were measured with a gas sampling system that stepped sequentially through two composite sample locations in each barn or room (8 total), with 6 minutes of sampling and analysis per location to ensure stabilized readings. In addition, gaseous concentrations of the ambient air or background were measured every two hours. The static pressures and fan status were used with fan-specific performance curves developed from in-situ measurements to determine each fan’s airflow rate, hence the building ventilation rate.
The average daily emissions from each source – breeding/early gestation (B/EG) barn, late gestation (LG) barn, farrowing barns, external manure storage, and farm-level overall, in pounds per 100 sows per day, is summarized in Table 1. The results show that methane emissions from the shallow-pit farrowing barns are 18% of those from the external manure storage and 0.11-0.12% of those from the deep-pit breeding/gestation barns. The farm-level daily CH4 (0.28 lb/sow-d) and N2O (5.2 ×10-4 lb/sow-d) emissions were equivalent to 7.3 lb CO2eq/sow-d. Majority (~94%) of the farm-level CO2 emission (8.2 lb/sow-d) is from animal respiration. Daily ammonia emissions averaged 0.03 lb/sow in the B/EG phase, 0.03 lb/sow-d in the LG phase, 0.074 lb/(sow+litter)-d in the farrowing phase, and 0.007 lb/(sow+litter)-d for the external manure storage, with an overall farm total of 0.033 lb/sow-d. Based on the daily farm-level ammonia emissions obtained from this study, the number of animals needed to trigger the EPA CERCLA reporting threshold of 100 lb NH3/d ranges from 3523 gestation sows to 1233 farrowing sows and litters for the manure handling systems involved in the study.
The measured emission rates from the LG and B/EG barns are higher than measured values from other breeding/gestation systems. This is due to previous measurements being taken on shallow pit buildings. The deep-pit manure storage results in more methane and nitrous production as manure is the main source of these two gasses in swine production systems. This is further evidenced by the drastically higher methane emissions from the external manure storage compared to the farrowing barns.