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. Chinese agricultural fertilizer (CAF), which is widely used in China, is the nation’s largest source of NH₃ emissions. The quantity, geographic distribution and historical trends of these emissions remain largely uncertain. In this paper, a new CAF 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) time trends were derived for 1978-2008 in which the spatial and temporal patterns and the uncertainties associated with the inventory were quantified; 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 NOx, SO₂ and NH₃ emissions.