GHG Emission from N Fertilizer Manufacture.
As is the case with NH3 synthesis, a range of different processes are used in the manufacture of specific fertilizer products. We included five N fertilizer products in this study: urea; AN; ammonium bicarbonate (ABC); ammonium chloride; and compound fertilizers containing N, phosphorus, and potassium (NPKs). We used the specific energy consumption rate of each product determined by the CNFIA survey and by Fan etal. (36) and estimated a GHG emission factor for each (Table S5). The CO2 fixed during the production of urea and ABC is emitted later into the atmosphere when the fertilizers are applied in the field; thus, it was not included in the calculations.