Comprehensive quantification of global cropland ammonia emissions and potential abatement.

Ammonia (NH) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8-31.2 Tg N yr during 1996-2013 with the increase rate of 1.6% yr. Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH emissions will decline by 26% from 2010 to 2100 given a 0.5% yr decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH emissions by up (71%, 17.6 Tg N yr) at an abatement cost of US$524 billion. Our findings indicate that cropland NH emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH abatement strategies.