Ammonia Emissions May Be Substantially Underestimated in China.

China is a global hotspot of atmospheric ammonia (NH) emissions and, as a consequence, very high nitrogen (N) deposition levels are documented. However, previous estimates of total NH emissions in China were much lower than inference from observed deposition values would suggest, highlighting the need for further investigation. Here, we reevaluated NH emissions based on a mass balance approach, validated by N deposition monitoring and satellite observations, for China for the period of 2000 to 2015. Total NH emissions in China increased from 12.1 ± 0.8 Tg N yr in 2000 to 15.6 ± 0.9 Tg N yr in 2015 at an annual rate of 1.9%, which is approximately 40% higher than existing studies suggested. This difference is mainly due to more emission sources now having been included and NH emission rates from mineral fertilizer application and livestock having been underestimated previously. Our estimated NH emission levels are consistent with the measured deposition of NH (including NH and NH) on land (11-14 Tg N yr) and the substantial increases in NH concentrations observed by satellite measurements over China. These findings substantially improve our understanding on NH emissions, implying that future air pollution control strategies have to consider the potentials of reducing NH emission in China.