Decoupling between ammonia emission and crop production in China due to policy interventions.

Cropland ammonia (NH ) emission is a critical driver triggering haze pollution. Many agricultural policies were enforced in past four decades to improve nitrogen (N) use efficiency while maintaining crop yield. Inadvertent reductions of NH emissions, which may be induced by such policies, are not well evaluated. Here, we quantify the China's cropland-NH emission change from 1980 to 2050 and its response to policy interventions, using a data-driven model and a survey-based dataset of the fertilization scheme. Cropland-NH emission in China doubled from 1.93 to 4.02 Tg NH -N in period 1980-1996, and then decreased to 3.50 Tg NH -N in 2017. The prevalence of four agricultural policies may avoid ~3.0 Tg NH -N in 2017, mainly located in highly fertilized areas. Optimization of fertilizer management and food consumption could mitigate three-quarters of NH emission in 2050 and lower NH emission intensity (emission divided by crop production) close to the European Union and the United States. Our findings provide an evidence on the decoupling of cropland-NH from crop production in China and suggest the need to achieve cropland-NH  mitigation while sustaining crop yields in other developing economies.