A national inventory for the United States of seasonally and geographically resolved ammonia emissions from dairy cows

Previous inventories of ammonia emissions have not characterized. seasonal and geographic variations in emission factors. We combined a model of manure management on a single dairy farm with a national survey of management practices to estimate the seasonal and geographic variation in ammonia emissions from dairy farms. Monthly, county-level emission factors were estimated. The annual emission factors were estimated to range between 13.1 and 55.5 kg NH3 cow(-1) year(-1), and the seasonal variation was estimated to be as high as a factor of seven in some counties. Emission factors were estimated to be highest in the summer and in southern and western states. However, the emission factors presented primarily were derived from field studies on European farms. Future field studies should focus measuring the seasonal variation of ammonia emissions from farming practices and conditions prevalent in the United States.