An ammonia emission inventory for fertilizer application in the United States

Fertilizer application represents a significant fraction of ammonia emissions from all sources in the United States. Previously published ammonia inventories have generally suffered from poor spatial and temporal resolution, erroneous activity levels, and highly uncertain emission factors. Here we present an ammonia emission inventory for fertilizer application that for the first time incorporates county-level data at monthly resolution, and includes more accurate activity levels and emission factors. The inventory shows that considerable variations in emissions can occur within a state. The emissions generally peak at two times of the year, in spring and in fall. The timing of these peaks depends on crop schedules. Overall, the new inventory shows the importance of determining emissions at sub-annual time resolution, and at spatial resolution better than statewide average values as reported in previous inventories.