典型人为和自然成因氨的氮同位素组成研究

Ammonia is an important promoter of air pollution, and ammonium deposition is the main form of atmospheric nitrogen deposition in many areas. Nitrogen isotope can be tracer the sources of atmospheric ammonia and ammonium. However, nitrogen isotope data of ammonia from different sources are scarce, especially in China, which is a bottleneck problem to tracer and distinguish the source of atmospheric ammonia and ammonium with nitrogen isotope for a long time. In this project, we selected typical anthropogenic sources (agricultural fertilizer, livestock farming, biomass burning, coal, waste water, waste disposal, vehicle exhaust) and natural sources (soil and marine volatile release) of ammonia as the research object. We analysis characteristics of nitrogen isotope composition and seasonal variation of ammonia from different sources, and investigate key environmental factors to influence nitrogen isotope fractionation during ammonia volatilization by controlling the experiments. This study aims to provide scarce isotope data to understand the atmospheric processes and mechanisms of different sources of atmospheric ammonia and to quantify the sources of atmospheric ammonium. Also, it can enrich application of the methods and theories of nitrogen isotope geochemistry in atmospheric nitrogen deposition and nitrogen pollution studies.

氨气是大气污染的重要推手，而铵沉降是很多地区大气氮沉降的主要形式。氮同位素可以示踪大气氨和铵盐的来源，但不同成因氨的氮同位素数据非常稀少，尤其在中国仍然是空白，这是长期以来应用氮同位素示踪和区分大气氨和铵沉降来源的瓶颈问题。本项目以典型人为成因（农业施肥、畜牧业养殖、生物质燃烧、燃煤、废水、垃圾处理、机动车尾气）和自然成因（土壤挥发和海洋释放）的氨气为研究对象。详细分析不同成因氨气的氮同位素组成和季节变化特征，并通过控制实验探讨影响氨气挥发过程氮同位素分馏的关键环境因子。本项研究旨在为理解不同来源氨气的大气过程机制以及大气铵来源的定量示踪提供紧缺的同位素数据，能够丰富氮同位素地球化学方法理论在大气氮污染和氮沉降研究中的应用。

长期以来，挥发源氨气（动物废弃物和农业施肥）和化石源氮氧化物（燃煤和机动车尾气）一直被认为是大气铵态氮和硝态氮的主要来源。近年来，越来越多的研究表明燃烧源氨气（燃煤、生物质燃烧、机动车尾气等）和非化石源氮氧化物（生物质燃烧、微生物氮循环）对大气铵态氮和硝态氮具有重要贡献。因此，准确区分挥发源氨气和燃烧源氨气对大气铵态氮的贡献、化石源氮氧化物和非化石源氮氧化物对大气硝态氮的贡献，对区域大气活性氮的减排具有重要意义。在本项目的资助下，我们测量了中国主要排放源氨气的氮同位素特征值并整合了全球主要排放源氮氧化物的氮同位素特征值，同时探讨了氨气向铵根离子转化的氮同位素效应和二氧化氮向硝酸根离子转化的氮同位素效应，并结合同位素质量平衡原理，区分了燃烧源和挥发源氨气对降水和颗粒态铵根离子的贡献，以及化石源和非化石源氮氧化物对降水和颗粒态硝酸根的贡献，最终阐明了燃烧源氨气和非化石源氮氧化物对大气铵态氮和硝态氮的重要性。这为大气活性氮减排提供科学依据