Improved Estimates of Ammonia Emissions from Global Croplands

Reducing ammonia (NH₃) volatilization from croplands while satisfying the food demand is strategically required to mitigate haze pollution. However, the global pattern of NH₃ volatilization remains uncertain, primarily because of the episodic nature of NH₃ volatilization rates and the high variation of fertilization practices. Here, we improve a global estimate of crop-specific NH₃ emissions at a high spatial resolution using an updated data-driven model with a survey-based dataset of the fertilization scheme. Our estimate of the globally averaged volatilization rate (12.6% ± 2.1%) is in line with previous data-driven studies (13.7 ± 3.1%) but results in one-quarter lower emissions than process-based models (16.5 ± 3.1%). The associated global emissions are estimated at 14.4 ± 2.3 Tg N, with more than 50% of the total stemming from three stable crops or 12.2% of global harvested areas. Nearly three-quarters of global cropland-NH₃ emissions could be reduced by improving fertilization schemes (right rate, right type, and right placement). A small proportion (20%) of global harvested areas, primarily located in China, India, and Pakistan, accounts for 64% of abatement potentials. Our findings provide a critical reference guide for the future abatement strategy design when considering locations and crop types.