Ammonia Emissions May Be Substantially Underestimated in China

摘要

China is a global hotspot of atmospheric ammonia (NH_3) emissions and, as a consequence, very high nitrogen (N) deposition levels are documented. However, previous estimates of total NH_3 emissions in China were much lower than inference from observed deposition values would suggest, highlighting the need for further investigation. Here, we reevaluated NH_3 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_3 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 4096 higher than existing studies suggested. This difference is mainly due to more emission sources now having been included and NH_3 emission rates from mineral fertilizer application and livestock having been underestimated previously. Our estimated NH_3 emission levels are consistent with the measured deposition of NH_x. (including NH_4~+ and NH_3) on land (11—14 Tg N yr~(-1)) and the substantial increases in NH_3 concentrations observed by satellite measurements over China. These findings substantially improve our understanding on NH_3 emissions, implying that future air pollution control strategies have to consider the potentials of reducing NH_3 emission in China.