Emission Factors Along the N Fertilizer Chain.For every ton of N produced and used on cropland in China, an average of 13.5 t of CO2-equivalent (eq) (t CO2-eq) is emitted (Fig. 1). The largest emission along the chain comes from ammonia synthesis (weighted average of 5.1 t CO2-eq, 37.8% of 13.5 t). This is partly due to the energy-intensive nature of the chemical engineering
process that requires high temperature and pressure and partly due to the low energy efficiency of coal as the main energy source. Coal-based facilities have an emission factor of>5tCO2 -eq t NH3-N −1 compared with