中国氮磷钾肥制造温室气体排放系数的估算

通过收集、整合国内相关数据,推算了符合中国目前情况的各种氮肥、磷肥和钾肥的制造过程中的温室气体排放系数(从原料到工厂大门)。结果显示,我国平均水平的氮肥制造碳排放系数为:合成氨(液氨)1.672 t CE/t N,尿素2.041 t CE/t N,碳铵1.928 t CE/t N,硝酸铵4.202 t CE/t N,氯化铵2.220 t CE/t N,氮肥综合系数为2.116 t CE/t N。我国一般水平的磷肥制造碳排放系数为:重钙0.467 t CE/t P2O5,磷酸二铵1.109 t CE/t P2O5,磷酸一铵0.740 t CE/t P2O5,普钙0.195 t CE/t P2O5,钙镁磷肥2.105 t CE/t P2O5,磷肥综合系数为0.636 t CE/t P2O5。我国先进水平的钾肥制造碳排放系数为:氯化钾0.168 t CE/t K2O,硫酸钾0.409 t CE/t K2O(其中罗钾法硫酸钾0.443 t CE/t K2O、曼海姆法硫酸钾0.375 t CE/t K2O),钾肥综合系数为0.180 t CE/t K2O。我国大部分氮磷钾肥的温室气体排放系数普遍为欧美平均水平的2倍左右,因此利用国外系数来估算我国的农业温室气体排放量将严重低估化肥施用的影响。

Estimation of greenhouse gases emission factors for China's nitrogen, phosphate, and potash fertilizers

As fossil fuel based chemical products, synthetic fertilizers are highly energy-intensive and therefore highly carbon-intensive products as well. Fertilizers are one of the most important modern agricultural materials for enhancing crop yields. The manufacture of fertilizers is also a considerable indirect greenhouse gases (GHGs) emission source related to agricultural activities. To feed its huge population, China has raised its average fertilizer application level from 86.7 kg/hm² in 1980 to 346.1 kg/hm² in 2010 (total N, P₂O₅ and K₂O). China has been the largest fertilizer producer and consumer worldwide for ten years, and its fertilizer consumption has exceeded 4.76 ×10⁷ t, almost one third of the world''s total, since 2005. Thus, it is essential to evaluate the GHGs emission related to the production and consumption of synthetic fertilizers in China. However, most current Life-Cycle Analysis (LCA) studies on China''s agricultural GHGs emission use foreign fertilizer emission factors (GHGs per unit of fertilizer product) because the actual domestic factors were not available, which might result in significant miscalculations and uncertainties. To solve this problem, we collected data specific to China''s fertilizer manufacture and consumption, and then estimated GHGs emission factors for several types of nitrogen, phosphate, potash and compound fertilizer currently in use in China. These fertilizers were: ammonia, urea, ammonium bicarbonate(AB), ammonium nitrate(AN), ammonia chloride(AC), general nitrogen fertilizer (General-N), triple superphosphate (TSP), monoammonium phosphate (DAP), monoammonium phosphate (MAP), superphosphate (SSP), fused calcium magnesium phosphate (FCMP), general phosphate fertilizer (General-P), potassium chloride (PC), general potassium sulphate (PS), Lop-Lake-method potassium sulphate (PS-LopLake), (PS-Mannheim) and general potash fertilizer (General-K). Our emission factors accounted for CO₂, CH₄ and N₂O released not only during manufacturing, but also from feedstock production and transportation outside factories (i.e. "from cradle to factory gate"). Due to the availability of different data, emission factors for N/P/K fertilizers were calculated using different methods, and thus represent different technological scenarios (N fertilizers: China''s current average technical level. P fertilizers: China''s current ordinary technological level, slightly behind the "average level", representing the nation''s target for energy-saving. K fertilizers: China''s current advanced technological level, representing the best potash factories with highest energy efficiency in China). China''s average-level nitrogen fertilizer manufacturing GHGs emission factors were: ammonia 1.672 t CE/t N, urea 2.041 t CE/t N, AB 1.928 t CE/t N, AN 4.202 t CE/t N, AC 2.220 t CE/t N and General-N 2.116 t CE/t N. China''s ordinary-level phosphate fertilizer manufacturing GHGs emission factors were: TSP 0.467 t CE/t P₂O₅, DAP 1.109 t CE/t P₂O₅, MAP 0.740 t CE/t P₂O₅, SSP 0.195 t CE/t P₂O₅, FCMP 2.105 t CE/t P₂O₅ and General-P 0.636 t CE/t P₂O₅. China''s advanced-level potash fertilizer manufacturing GHGs emission factors were: PC 0.168 t CE/t K₂O, PS 0.409 t CE/t K₂O, PS-LopLake 0.443 t CE/t K₂O, PS-Mannheim 0.375 t CE/t K₂O and General-K 0.180 t CE/t K₂O. As a result of the more complete LCA chain investigated in this study, different natural resource availability and distribution traits, energy structure, and technological levels, most fertilizers'' GHGs emission factors in China were about 2-fold of those in western countries. Thus, the models using western factors to calculate China''s agricultural GHGs emissions will significantly underestimate the impact of fertilizer application.