High-resolution inventory of ammonia emissions from agricultural fertilizer in China from 1978 to 2008

Abstract. The quantification of ammonia (NH₃) emissions is essential to the more accurate quantification of atmospheric nitrogen deposition, improved air quality and the assessment of ammonia-related agricultural policy and climate mitigation strategies. The quantity, geographic distribution and historical trends of these emissions remain largely uncertain. In this paper, a new Chinese agricultural fertilizer NH₃ (CAF_NH₃) emissions inventory has been compiled that exhibits the following improvements: (1) a 1  ×  1 km gridded map on the county level was developed for 2008; (2) a combined bottom-up and top-down method was used for the local correction of emission factors (EFs) and parameters; (3) the temporal patterns of historical time trends for 1978–2008 were estimated and the uncertainties were quantified for the inventories; and (4) a sensitivity test was performed in which a province-level disaggregated map was compared with CAF_NH₃ emissions for 2008. The total CAF_NH₃ emissions for 2008 were 8.4 TgNH₃ yr⁻¹ (a 6.6–9.8 Tg interquartile range). From 1978 to 2008, annual NH₃ emissions fluctuated with three peaks (1987, 1996 and 2005), and total emissions increased from 3.2 to 8.4 Tg at an annual rate of 3.0 %. During the study period, the contribution of livestock manure spreading increased from 37.0 to 45.5 % because of changing fertilization practices and the rapid increase in egg, milk, and meat consumption. The average contribution of synthetic fertilizer, which has a positive effect on crop yields, was approximately 38.3 % (minimum: 33.4 %; maximum: 42.7 %). With rapid urbanization causing a decline in the rural population, the contribution of the rural excrement sector varied widely between 20.3 % and 8.5 %. The average contributions of cake fertilizer and straw returning were approximately 3.8 and 4.5 %, respectively, thus small and stable. Collectively, the CAF_NH₃ emissions reflect the nation's agricultural policy to a certain extent. An effective approach to decreasing PM_2.5 concentrations in China would be to simultaneously decrease NO_x, SO₂, and NH₃ emissions.