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.