Ammonia Emissions May Be Substantially Underestimated in China

China is a global hotspot of atmospheric ammonia (NH₃) emissions and, as a consequence, very high nitrogen (N) deposition levels are documented. However, previous estimates of total NH₃ emissions in China were much lower than inference from observed deposition values would suggest, highlighting the need for further investigation. Here, we reevaluated NH₃ 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 NH₃ emissions in China increased from 12.1 ± 0.8 Tg N yr⁻¹ in 2000 to 15.6 ± 0.9 Tg N yr⁻¹ 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 NH₃ emission rates from mineral fertilizer application and livestock having been underestimated previously. Our estimated NH₃ emission levels are consistent with the measured deposition of NHx (including NH₄⁺ and NH₃) on land (11-14 Tg N yr⁻¹) and the substantial increases in NH₃ concentrations observed by satellite measurements over China. These findings substantially improve our understanding on NH₃ emissions, implying that future air pollution control strategies have to consider the potentials of reducing NH₃ emission in China.