Seasonal ammonia emissions from an intensive beef cattle feedlot in Victoria Australia

Ammonia (NH₃) emitted from concentrated animal feeding operations can cause environmental and health problems, and indirectly contribute to greenhouse gas emissions. Cattle feedlots are known to be large sources of NH₃, but few studies have documented seasonal emissions from Australian feedlots. We conducted two field campaigns to measure NH₃ emissions from an intensive beef cattle feedlot in southeast Australia, and these results were combined with previous measurements at the same feedlot to document seasonal variations in emissions and to derive annual feedlot emission factors (EFs). Emission rates were calculated with an inverse dispersion modelling (IDM) technique, based on NH₃ concentrations measured at the feedlot with open-path lasers (OPLs). The average area emission rates in spring, summer, autumn and winter were 90.5, 167.4, 96.2 and 86.8 μg NH₃ m^-2 s^-1 from the cattle pens, and 22.5, 18.1, 7.7 and 20.7 μg NH₃ m^-2 s^-1 from the manure stockpile area, respectively. The total per-animal EFs ranged from 126.0 (autumn) to 190.2 g NH₃ animal^-1 d^-1 (summer), representing a loss of 47.5-64.6% of the fed N. Seasonal variations in emissions were related to air temperature. Slight changes in crude protein content of the cattle diet may also have impacted seasonal variability. Taking seasonal variations into consideration, the average feedlot EF was 160.4 g NH₃ animal^-1 d^-1, with 90% of the emissions coming from the cattle pens. Extrapolating the EF to all feedlot cattle in the country, the direct NH₃ emissions from Australian feedlots amount to 65.2 Gg NH₃ annually, or 3.7% of the national total. Our study benchmarks seasonal and annual EFs and N losses for Australian commercial feedlots, and provides a baseline for extrapolating the impacts of mitigation efforts.