Well-managed urbanization could halve nitrogen pollution in China

Halving nitrogen pollution is crucial for achieving sustainable development goals (SDGs). However, how to reduce nitrogen pollution from multiple sources remains a grand challenge. Here we show that reactive nitrogen (N r ) pollution could be roughly halved by well-managed urbanization in China by 2050, with emissions of NH 3 , NO x and N 2 O to air declining by 44%, 30% and 33%, respectively, and N r to water bodies by 53%. Urbanization shifts population from rural to urban areas and promotes large-scale and crop-livestock coupled farming, which reduces non-point source pollution from rural sewage and agriculture. Although rural-to-urban migration increases point-source nitrogen emissions in metropolitan areas, regional air and water quality can be improved by reducing upstream and regional total N r losses, with increased opportunities to control of point source emissions vs. diffuse emissions. Approximate US$ 61 billion would be required for additional urban waste treatment, agricultural land consolidation and livestock relocation, as well as upgrading industrial facilities. However, the overall benefits are calculated at US$ 245 billion due to increases in agricultural productivity and improvements in environmental quality. Such a large benefit-to-cost ratio suggests the feasibility and cost-effectiveness of halving N r pollution through urbanization, and this would make significant contributions to achieving several SDG targets.