大气氮沉降数值模拟的演替进程与模型筛选

Numerical modeling atmospheric nitrogen deposition:evolution process and models' screening

中国是维持全球氮平衡的关键。以大气氮沉降为例,畜禽养殖、化肥施用、能源消耗等人为扰动致使活性氮的排放量与沉降量正持续走高,欧美已率先开展氮沉降及其引发的环境与经济后果的评估。中国省级或更大尺度的沉降规模,空间分布和输移途径资料较难获取,大气传输模型(ATMs)提供了经济可行的解决方案。通过概述ATMs的演进阶段和代表模型,并为应对我国缺乏氮沉降模拟专业模型的问题,建立一个总量近百的大气氮沉降相关模型(排放源含NH_3、NOx和SO_2的ATMs),以总揽世界模型发展全貌。理论上,模型的检验和相互比较以监测值与模拟值的定性分析为基础,中国面临的困境缺乏全国性的统一监测网络在短期内难以解决。事实上,大气氮沉降模型在污染场和浓度场的模拟过程中受到诸如大气环流、边界层高度等条件的制约进而影响模拟效果。NH_3的特性对模型提出了更高要求。一方面通过参考相关文献归纳各种制约条件的相对重要性,另一方面结合模型自身架构(格网大小、垂直精度、气象场获取途径以及扩散模式的选取)、模拟过程(源排放、干沉降和扩散)、设计意图,力图以定性或半定量的方法探讨各个模型应对制约条件的能力,比较各自优劣,以期筛选出适用于模拟省域乃至全国大气氮沉降的数值模型。

China is pivotal in determining the global nitrogen（N）balance in terms of nitrogen deposition. Multifari- ous anthropogenic perturbations, e.g. livestock and poultry breeding, N fertilizer application and fossil fuel combus- tion have been contributing substantial amounts of Nr emission as well as deposition. EU and US leading the field on assessment of N deposition and its environmental or economic consequences. Comparatively, the magnitude, spatial distribution and transportation patterns of the terrestrial nitrogen deposition in China remain uncertain and need to investigated provincially and nationally. The atmospheric transport models （ATMs）are regarded as an economic and feasible instrument for the ability of characterizing and predicting nitrogen deposition. In response to the ab- sence of a specialized N deposition model in China, we established an N-related deposition models （NDMs）informa- tion base, which covered all ATMs worldwide in which NH3,NOx and SO2 emission sources involved, aiming to pres- ent an comprehensive overview and critical discussion on the state of the science of NDMs. Theoretically, models＇ validation and inter-comparison depend on the quantitative analysis of monitoring data against modeling data. How- ever, the scarcity of unified monitoring network in China posed an insurmountable obstacle to implementation. In fact, the atmosphere is a complex and dynamic system that interacts significantly with the land, water body and plant canopy. It is noted that the NDMs to predict atmospheric concentration and deposition fields of nitrogen are subject to numerous constraints and uncertainties, e.g. meteorological field, circulation patterns and boundary layer height, which will influence the modeling performance more or less. Meanwhile, NH3 raises additional demands on the mod- els. Therefore, here we tentatively indicated the factors for the differences in models＇ performance in terms of the model construction（focused on the grid size, vertical resolution, meteorological field access and the fundamental dif- ference between Eulerian and Lagrangian models）, modeling processes （of particular concerning emissions, dry de- position and diffusion）and R ＆ D （Research and Development）original intentions （different initial purposes and pri- orities setting）. The objective of this study was to evaluate the relative merits of NDMs in a qualitative way, screen out several sound modes for Chinese N deposition modeling at a provincial or national scale in the future.