Tracking Carbon and Ammonia Emission Flows of China's Nitrogen Fertilizer System: Implications for Domestic and International Trade.

China is the world's largest producer, consumer, and exporter of synthetic nitrogen (N) fertilizer. To assess the impact of domestic demand and international exports, we quantified the life-cycle CO₂eq and ammonia (NH₃) emissions by tracking carbon (C) and nitrogen (N) flows from coal/gas mining through ammonia production to N fertilizer production, application, and export. In 2020, China's N fertilizer system emitted 496.04 Tg of CO₂eq and 3.74 Tg of NH₃, with ammonia production and N fertilizer application processes contributing 36 and 85% of the life-cycle CO₂eq and NH₃ emissions, respectively. As the largest importers of N fertilizer, India, Myanmar, South Korea, Malaysia, and the Philippines collectively shifted 112.41 Tg of CO₂eq. For every ton of N fertilizer produced and used in China, 16 t of CO₂eq and 0.18 t of NH₃ were emitted, compared to 9.7 t of CO₂eq and 0.13 t of NH₃ in Europe. By adopting currently available technologies, improving N fertilizer utilization efficiency and employing nitrification inhibitors could synergistically reduce CO₂eq emissions by 20% and NH₃ emissions by 75%, while energy transformation efforts would primarily reduce CO₂eq emissions by 59%. The production of ammonia using green electricity or green hydrogen could significantly enhance the decarbonization of China's N fertilizer system.