Recently, research by Dr. Liao Wenling (State Key Joint Laboratory of Environmental Simulation and Pollution Control, Department of Environmental Science, Peking University) was published in Science China Earth Sciences. By improving the estimation method of ammonia emission inventory and the consideration of ammonia emission sources, a comprehensive county-level ammonia emission inventory with high spatial and temporal resolution in China was compiled, and the sources as well as the temporal and spatial variations of ammonia emissions were analyzed.