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题名	大气中N2O源汇机制研究
作者	刘侃侃
学位类别	博士
答辩日期	2014-05
授予单位	中国科学院研究生院
授予地点	北京
导师	牟玉静
关键词	N2O O(1D) 源和汇 光化学 同位素异常 N2O O(1D) source and sink photochemistry isotope anomaly
其他题名	Study on Atmospheric N2O Formation & Consumption
学位专业	环境科学
中文摘要	氧化亚氮（N2O）是大气中重要的温室气体之一，也是参与平流层臭氧损耗的一种关键物质。大气中N2O 目前被认为主要来自地表微生物的硝化和反硝化过程，其在大气中的消耗主要发生在平流层的光解和与激发态氧原子（O(1D)）的反应。但同位素测定结果表明大气中N2O 存在明显重同位素分馏现象，且氧同位素表现为质量无关异常现象，从而对N2O 的现有大气化学认识提出质疑。为解释大气中N2O 氧同位素质量无关异常现象，人们提出了多种源自O3 的光化学反应机制，但大多机制已被实验证据所否认。此外，采用当前N2O 大气化学的已有认识，目前还无法解释北半球NO2 的年增长率远远低于N2O 的年增长率以及大气化学模型对低平流层活性氮物种（NOy）低估现象。为此，本文利用聚四氟乙烯薄膜气袋在253.7 nm 低压汞灯辐射下系统研究了N2O 在氮气和氧气光化学反应体系中的产生与消耗，以期探索大气中N2O 的光化学源汇机制，并取得了以下主要研究结果： （1）发现现有化学反应动力学数据无法解释N2O 在氮气和氧气光化学反应体系中的快速产生速率：O(1D) + N2 + M 在室温（298 K）条件下反应生成N2O速率比基于已有动力学数据估算值高两个数量级以上。通过温度系列实验研究得出该反应的三级速率常数与温度的阿伦尼乌斯表达为： k(T)=1.06×10-38exp(3374/T) cm6 molecule-2 s-1，由此估算该反应对大气中N2O 的源强比目前全球N2O 源排放强度估算值高约4 倍。 （2）基于本研究的实验现象以及文献报道的异常结果，合理推测了激发态氧原子O(1D)与N2 分子碰撞结合所形成的高激发态N2O*与O2 分子的碰撞可能是形成稳态N2O 的主要通道，且稳态N2O 中的氧原子可能主要来自于O2，从而可解释N2O 氧同位素质量无关的异常现象：N2O* + O2 → (N2O*···O2) → N2O* +O* + O。 （3）发现近实际大气条件下光反应体系中O(1D)与N2O 反应所消耗N2O 速率比实际观测值低两个数量级以上，因此，推测大气中存在N2O 未认知的消耗途径。基于本实验结果及文献资料，提出振动激发态O2*与N2O 反应可能会形成一种过渡复合物中间体，该中间体类似N2O3 可以吸收紫外辐射光，从而可导致N2O 的破坏，即：2 2 2 2 N O + O * (N O O *)hv    products并初步估算出由激发态O2*和N2O的反应所引起的N2O的消耗速率常数约为~2 ×10-16 cm3 molecule-1 s-1 以及大气中N2O的寿命可由目前所估的120 年缩减至约33年。
英文摘要	Nitrous oxide (N2O) is a potent greenhouse molecule as well as the major source of stratospheric NOy which catalyzes the loss of ozone in the stratosphere. The primary sources of N2O based on current knowledge are mainly emitted from edaphic and oceanic microbial activity as a by-product of nitrification and denitrification reactions, and the major sink is in its stratospheric ultraviolet photolysis and reaction with electronically excited oxygen atoms, O(1D). The atmospheric concentration of N2O is about 326 ppbv and increasing at a rate of 0.26% per year. Even though considerable progress has been made in recent years in the identification of new in-situ sources, the uncertainties associated with individual sources have not been reduced. In addition, the recent discovery of isotope anomalies in atmospheric N2O and the remarkably increase trend of NO2 in the northern hemisphere have also cast doubts on the current understanding of the global N2O budget. Several possible atmospheric N2O sources stemming from O3 have been proposed for explaining such anomalies of atmospheric N2O, however, most of proposed atmospheric formation sources have been ruled out by experimental evidences. Therefore, the production and consumption of N2O in various gas mixtures were systemically investigated in this study under irradiation of eight filtered low pressure Hg lamps with central wavelength of 253.7 nm and the results present as shown below. 1st, experimental evidences in this work showed that previes estimation of the global N2O source strength via the reaction of excited oxygen (O1D) with N2 was significantly underestimated. Assuming that all observed N2O comes from the O(1D)+ N2 + M  N2O + M reaction, the temperature dependent rate coefficient for the reaction is well described by the Arrhenius expression: k(T)=1.06×10-38 exp(3374/T) cm6 molecule-2 s-1. The k(298 K) is at least two (or three) orders of magnitude faster than previously four measured data at 298 K, and the global N2O source strength from the reaction is about a factor of 4 greater than the current estimation for the global N2O source strength . 2nd, the reaction of O2 with excited transitional states of N2O* which collided and combined between O(1D) and N2 (N2O*+O2→N2O*···O2→N2O+O*+O) was found to be the main reaction channel relative to the reaction of N2+N2O* and, the O atom may be exchanged between O2 and excited N2O*. The mechanism of the complex formation between the highly excited N2O* and O2 was rationally proposed to explain the mass independent anomaly of atmospheric N2O. 3rd, atmospheric N2O consumption rate via the reaction of N2O with excited O2* under UV irradiation (N2O+O2*→N2O···O2* hv  products) was found to be comparable to the N2O formation rate. The rate coefficient for the reaction is estimated approximately to be ~2×10-16 cm3 molecule-1 s-1 and thus the atmospheric N2O life should be 33 years rather than 114 years. In addition, the mechanism of the complex formation between the excited O2* and N2O was also rationally proposed to explain the mass independent anomaly of atmospheric N2O and the unexpectedly fast consumption of N2O by the excited O2*.
公开日期	2015-06-16
内容类型	学位论文
源URL	[http://ir.rcees.ac.cn/handle/311016/13481]
专题	生态环境研究中心_大气环境科学实验室
推荐引用方式 GB/T 7714	刘侃侃. 大气中N2O源汇机制研究[D]. 北京. 中国科学院研究生院. 2014.

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