【作者】 张秋菊；

【导师】 陈建民；

【作者基本信息】 复旦大学 ， 环境科学， 2006， 博士

【摘要】 大气颗粒物或气溶胶对全球气候、人类健康和地球环境影响巨大。SO₂是大气中最主要的人类污染物，也是形成酸雨和硫酸盐气溶胶的前体之一，影响生态环境和人类健康。其在大气中可以通过云层和液滴氧化转化成硫酸和硫酸盐粒子，也可以与气溶胶粒子发生复相反应形成含硫酸根的二次气溶胶，而后者的转化机理和转化能力尚未被完全认识。气溶胶中的铁是许多大洋海区中海洋表层水中的浮游生物所必需的微量营养物的主要来源，在很多海区，尤其在某些高氮低铁海区，矿物气溶胶中的铁是这些地区海洋生产力的限制因素。基于以上原因，人们对SO₂与气溶胶，尤其是含铁气溶胶的复相反应及可溶性铁的来源非常关注。本论文通过实验室模拟SO₂与Fe₂O₃及Fe₂O₃和NaCl混合颗粒物的复相反应来探讨气溶胶中的铁在SO₂复相反应中的作用及反应机理，分为三个主要部分：第一部分选择和优化了反应产物Fe（Ⅱ）的测定方法。在综述Fe（Ⅱ）测定方法的基础上，确定用反相高效液相色谱法测定复相反应产物，对测定条件进行优化。得出最佳实验条件并使用pH5.6琥珀酸-硼砂缓冲溶液直接提取复相反应产物中Fe（Ⅱ），六次测定RSD为3.48％，回收率为90-102％，精密度及准确度均较好，此法用于复相反应产物Fe（Ⅱ）的测定。第二部分重点研究了SO₂与Fe₂O₃复相反应机理。利用DRIFT、XPS、HPLC、IC和pH计对反应产物进行了定性和定量分析，结果表明：SO₂与Fe₂O₃的复相反应可以产生Fe（Ⅱ）（aq）和SO₄^2-，表面吸附水有利于Fe（Ⅱ）（aq）和SO₄^2-的生成。SO₂浓度增加，Fe₂O₃表面酸度增加，可溶性Fe（Ⅲ）（aq）、Fe（Ⅱ）（aq）及SO₄^2-含量随之增加。室温下（T=291 K，RH=68％），每毫克Fe₂O₃在30min内可消耗53.6μg SO₂，生成12.6ng Fe（Ⅱ）（aq）和56.2μg SO₄^2-。反应产物SO₄^2-的浓度比三价铁被还原的产物Fe（Ⅱ）（aq）的浓度高出3个数量级，根据以上结果，提出Fe（Ⅱ）（aq）和硫酸盐的生成机理。同时表明Fe（Ⅱ）（aq）除了作为SO₂氧化的催化剂外，也是复相反应的产物之一。SO₂与Fe₂O₃的复相反应实验室模拟结果为大气海洋体系中，尤其是气溶胶在长距离传输中可能存在的铁硫耦合反馈机制提供了重要的实验依据。第三部分初步探讨了SO₂与Fe₂O₃和NaCl混合颗粒物复相反应机理。利用HPLC、IC和pH计对复相反应产物进行了定性和定量分析。结果表明：相对湿度大有利于Fe（Ⅱ）（aq）的生成；NaCl的加入有利于Fe（Ⅱ）（aq）的生成，但NaCl对SO₂与Fe₂O₃的反应有缓冲作用，随时间增加，反应体系的pH先下降后升高，Fe（Ⅱ）量增加，提取液中硫酸盐先达到最大，再下降而后平衡。根据测定结果初步探讨了复相反应产物形成机理。由于NaCl的存在，使海洋上空的铁硫耦合机制变得相当复杂。因此大气海洋中的铁和硫相互耦合机制是值得进一步探讨的可能影响全球气候变化的机制之一。更多还原

【Abstract】 Atmospheric particles or aerosols play an important role in global climate, human health and many aspects of earth environment. Sulfur dioxide, the principal sulfur-containing anthropogenic pollutant, acts as a precursor of sulfuric acid which contributes to acid rain and particulate sulfate. It can cause the adverse health effects and destroy the ecosystem. The oxidation of SO₂ in the atmosphere may occur in the gas phase, in the aqueous phase of clouds and fogs, and on the surface of aerosol particles, but the latter reaction mechanisms has not been elucidated in detail yet. Iron in aerosols is the major source of phytoplankton’s micronutrient in surface seawater. Moreover, it has been demonstrated to be the limiting nutrient factor for primary productivity especially in high nutrient, low chlorophyll （HNLC） regions.Based on above reasons, a better understanding of the heterogeneous reaction between SO₂ and aerosols, especially iron-containing dust, and the source of soluble iron is of interest.In this thesis, the heterogeneous reaction between SO₂ and Fe₂O₃ （or: Fe₂O₃ + NaCl） was investigated to explore the role of iron in oxidation of SO₂ and the reaction mechanism. In the first section, the determination method of Fe（II） by HPLC was selected , modified and the optimal condition was obtained. Fe（II） was extracted using succinic acid-disodium tetraborate buffer solution （pH5.6）. It can complex with the reagent ferrize to form [Fe（FZ）₃]²⁺, then determinate at 254 nm. RSD was 3.48% and the recovery was 90-102%. The concentration of Fe（II）, one of the heterogeneous reaction products, had been determined by this method.The second part is to study the heterogeneous reaction mechanism between SO₂ and Fe₂O₃. A combined technique of DRIFTS, XPS, HPLC, IC and pH meter is employed to demonstrate the formation of Fe（II）（aq） and SO₄^2- in the heterogeneous reaction between SO₂ and Fe₂O₃. The results revealed that absorbed water is the most crucial factor in the formation of Fe（II）（aq） and SO₄^2- Under ambient condition （T = 291 K, RH = 68 %） within 30 min, for 1 mg of Fe₂O₃ with the exhaustion of 53.6 μg SO₂, it could produce 12.6 ng Fe（II）（aq） and 56.2 μg SO₄^2- The concentration of the product [SO₄^2-], was three orders of magnitude higher than that of Fe（II）（aq）, indicating that large amount of SO₄^2- production was formed via catalysis by the transitional metal Fe. The reaction mechanism of SO₂ oxidation on Fe₂O₃ is proposed. It could be concluded clearly that Fe（II）（aq） is not only a catalyst involved in thisheterogeneous SO₂ oxidation , but also one of the end products of this heterogeneous reaction. This important finding provides the strong evidence to support the hypothesis of the coupling and feedback of iron with sulfur in aerosols during their long-range transport.The final part is a pilot study on the reaction mechanism between SO₂ and mixed particles of Fe₂O₃ and NaCl. The products were analyzed by HPLC、IC and pH meter. The results showed that the higher relative humility and the addition of NaCl were favorable for the formation of Fe（II）（aq）. A buffering role that prevented the pH from decreasing was found when NaCl presented. With the reaction time increasing, pH decreased and then increased; Fe（II） increased; SO₄^2- was formed rapidly, subsequently decreased and finally reached a plateau. A possible mechanism was proposed. The presence of NaCl complicates the coupling and the feedback of iron with sulfur in marine atmosphere. So Fe-S coupling and the possible positive feedback in marine atmosphere is an important mechanism which may affect the global climate change and is worthy to be further studied.更多还原