Seasonal ammonia emissions from a free-stall dairy in central Texas

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 x yr(-1) x head(-1) for summer and 4.7 +/- 4.9 kg-NH3 x yr(-1) x head(-1) for winter. The estimated annual NH3 EF was 8.4 +/- 4.9 kg-NH3 x 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.