Seasonal Ammonia Emissions from a Free-Stall Dairy in Central Texas

Abstract

Studies show that agricultural and animal feeding operations (AFOs) contribute a considerable amount of ammonia (NH₃) to the atmosphere. Agricultural NH₃ emissions are recognized as an important air quality issue. Biological decomposition of manure from dairy operations results in emissions of NH₃ and other gases. There is a need to determine NH₃ emission factors (EFs) to compile annual NH₃ inventories. NH₃ emissions should be estimated from different ground-level area sources (GLAS) including open-lots (cows on earthen corrals), free-stalls (cows in barns), manure composting sites, primary and secondary lagoons, separated solids, and milking parlors. A protocol using flux chambers was used to determine NH₃ EFs from different GLAS of a free-stall dairy in central Texas. Data including NH₃ emissions from GLAS were collected during winter and summer seasons. NH₃ concentration measurements were made using chemiluminescence-based analyzers. The EFs for the free-stall dairy were estimated as 11 ± 4.9 (confidence interval [CI]) kg-NH₃ · yr^-1 · head^-1 for summer and 4.7 ± 4.9 kg-NH₃ · yr^-1 · head^-1 for winter. The estimated annual NH₃ EF was 8.4 ± 4.9 kg- NH₃ · yr^-1 · head^-1 for this free-stall dairy. This seasonal difference was attributed to temperature, loading rate of dairy waste, and manure bacterial activity of GLAS. In winter, composted manure and free-stalls contributed nearly 77% of the total NH₃ emissions for the dairy; however, in summer, two lagoons at the dairy contributed 65% of the overall NH₃ emissions.