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

Ammonia (NH) is one of the main polluted gases in the atmosphere, and its emission has markedly increased in recent years. In China, NH is mainly emitted from agricultural fields. Using city-wide data on NH emissions in agricultural fields, the spatio-temporal emission of NH 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 NH emission in agricultural lands was 1623.0-1801.5 Gg/year. The rate of increase in NH emission in the period 2003-2015 was 0.74% per year, which was relatively stable. The leading sources of NH 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% NH emission in the study area, respectively. Hebei and Shandong provinces contributed the highest NH emission in North China. The contribution rate of NH emission in each province varied with sources, agricultural development, and population density. Based on the 1 km × 1 km grid resolution map for NH 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.