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 datadriven 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.

Automated summary

The study improved estimates of crop-specific NH3 emissions globally and highlighted the potential impact of improving fertilization schemes in reducing global cropland NH3 emissions by three-quarters. It also identified that a small proportion of global harvested areas, primarily in China, India, and Pakistan, have the potential to contribute to 64% of emissions reduction.