Spatio-temporal distribution of ammonia (NH₃) emissions in agricultural fields across North China

Ammonia (NH₃) is one of the main polluted gases in the atmosphere, and its emission has markedly increased in recent years. In China, NH₃ is mainly emitted from agricultural fields. Using city-wide data on NH₃ emissions in agricultural fields, the spatio-temporal emission of NH₃ was estimated for North China. This included emissions from nitrogen fertilizers, field straws, background soil, nitrogen-fixing plants, human feces, and livestock/poultry manure. Based on the results, the range of NH₃ emission in agricultural lands was 1623.0-1801.5 Gg/year. The rate of increase in NH₃ emission in the period 2003-2015 was 0.74% per year, which was relatively stable. The leading sources of NH₃ emission included the excessive use of chemical fertilizers in agriculture and the continuous expansion of livestock and poultry industries scale, accounting respectively for 44.9% and 43.9% NH₃ emission in the study area, respectively. Hebei and Shandong provinces contributed the highest NH₃ emission in North China. The contribution rate of NH₃ emission in each province varied with sources, agricultural development, and population density. Based on the 1 km × 1 km grid resolution map for NH₃ emission, the range and average of emission were 9.72-10.13 kg/ha and 9.95 kg/ha, respectively. High emissions were in the southeast of Hebei province and most of Shandong province. For these regions, there is a need for changes in policies relating to the use of chemical fertilizers in agriculture and the management methods of livestock production in the region.