Changes in production and fate of anthropogenic nitrogen driven by environmental policies in China

China's synthetic ammonia accounts for approximately 30% of global production and consumption of synthetic ammonia, suggesting that domestic shifts in allocation across fertilizer production, industrial intermediates, and environmental applications directly influence global nitrogen supply, trade flows, and environmental outcomes. However, limited statistical data on the sectoral allocation of reactive nitrogen across industrial end uses has hindered quantitative understanding of these changes as well as the trend forecasting. Here, we employed material flow analysis (MFA) to 210 enterprises and 34 downstream products to quantify production and end-use patterns over the past decade (2010-2020) and project future trends. The results indicated that the total synthetic ammonia production exhibited an inverted U-shaped fluctuation from 2010 to 2020, rising from 45.51 million tons in 2020 to a peak of 55.08 million tons in 2015, then declining to 49.19 million tons by 2020. Concurrently, the share directed to agricultural purposes decreased from 76.8% to 61.9%, while industrial allocation increased from 23.2% to 38.1%. These shifts were driven by environmental regulations, including the policy of "zero growth in chemical fertilizer use" in croplands and various air pollution controls, resulting in a 21.4% decline in N fertilizer consumption (e.g., urea, diammonium phosphate, and compound fertilizers) and rising industrial demand (e.g., for urea-formaldehyde resin and melamine). Projection analyses, for China specifically, suggest that total anthropogenic N production will stabilize at approximately 50 million tons by 2030 under continued policy enforcement, with agricultural use continuing to decline and industrial use increasing to roughly 26 and 24 million tons, respectively. Despite these insights, comprehensive research on the environmental impacts of this transition remains urgently needed.