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题名: 典型大气污染物与黑碳的非均相反应研究
作者: 赵燕1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 贺泓
关键词: 黑碳,污染气体,非均相反应,反应动力学 ; Soot, Gas pollutants, Heterogeneous reaction, Reaction kinetics
其他题名: Heterogeneous Reactions of Typical Gas Pollutants with Soot
学位专业: 环境科学
中文摘要: 黑碳主要来源于化石燃料和生物质不完全燃烧。大气中广泛存在的黑碳, 对空气质量和气候变化有重要影响。在大气中黑碳可与气体污染物发生非均相 反应,从而引起黑碳性质变化,并进一步影响其气候和环境效应。同时,非均 相反应也会影响气体污染物在大气中的转化。本论文考察了燃烧条件如燃氧比 和燃料含硫对黑碳组成、形貌和亲水性等的影响,利用衰减全反射红外光谱、 流动管反应装置和离子色谱研究了相对湿度(RH)和黑碳组成对 SO2与黑碳非均 相反应的影响、黑碳中有机碳(OC)和元素碳(EC)在 O3与黑碳非均相反应中的作 用以及 NO2与黑碳中 EC的反应。主要研究内容和结果如下: (1)在可控条件下,以正己烷为燃料制备了不同性质的黑碳样品,发现燃烧 条件对黑碳性质具有重要影响。OC中不饱和物种含量随燃氧比增大而增多,EC 中的缺陷位含量随燃氧比增大而增加。贫燃条件下,燃料含硫对黑碳性质有显著 影响。贫燃黑碳中硫酸盐总量随燃料硫含量非线性增加,而表面硫酸盐含量随燃 料硫含量线性增加。贫燃黑碳表面上的硫酸盐作为水吸附位点极大的增强了黑碳 的吸湿性。高含硫量的燃料有利于炔烃生成,从而使贫燃黑碳初级粒径增大和聚 集体数浓度增加。 (2)相对湿度显著影响 SO2与黑碳的非均相反应。在 RH为 6%-68%范围内, 吸附水增加促进了 SO2在黑碳上的吸附和硫酸盐生成;当 RH高于 80%时,过 量水则抑制 SO2的吸附和硫酸盐的生成。燃烧条件决定的黑碳表面组成在 SO2 与黑碳非均相反应中发挥了重要作用,并与相对湿度密切相关。黑碳表面吸附 的适量水和SO2有利于硫酸盐生成。在低 RH(6%)条件下,高燃氧比条件下(0.162) 制备的黑碳,由于可吸附 SO2的芳香 C−H基团含量较高,具有较大的 SO2摄 取容量;而在高 RH(54%)条件下,低燃氧比条件下(0.134)制备的黑碳表面具有 适量的 C=O基团和芳香 C−H基团,产生适量 SO2和水的吸附,从而使 SO2向 硫酸盐转化活性最高。高燃氧比条件下(0.162)制备的黑碳经 O3老化后,芳香 C−H基团减少并伴随 C=O官能团增加,导致其 SO2反应活性增强;而低燃氧 比条件下(0.134)制备的黑碳经 O3老化后 SO2反应活性降低。 (3) O3在黑碳上的反应活性与燃烧条件密切相关。随着燃氧比增大,O3在 黑碳上的初始摄取系数增加,并随 OC中的不饱和物种量线性增加。同时,O3 在 EC上的初始摄取系数随 EC的燃氧比增大而增加,并随 EC中缺陷位含量线 性增加。由此表明,燃烧条件决定黑碳中 OC的组成和 EC的结构,并会影响 黑碳与 O3的非均相反应活性。 (4)燃烧条件决定的 EC微观结构对 NO2在黑碳表面非均相反应具有重要 影响。NO2在 EC上的摄取系数和 HONO产率随燃氧比增大而增加,并与 EC 中缺陷位的含量线性相关。由此表明,EC中的缺陷位是 NO2反应与 HONO产 生的活性位点。经 O3室温老化和 O2在 300 °C氧化后,NO2在 EC上的摄取系 数和 HONO产率显著降低。然而,经 O2氧化后的 EC上 NO产率显著增加。 O2氧化后 EC上产生的醌型 C=O可将 NO2还原为 NO。
英文摘要: Soot particles, produced from incomplete fossil fuel burning and biomass combustion, are ubiquitous in the atmosphere and exert profound effects on air quality and climate. Soot particles are prone to heterogeneous reactions with gas pollutants after being emitted into the atmosphere, which can modify the properties of the particles, and subsequently influence the climatic and environmental effects of soot. Meanwhile, these heterogeneous processes can affect the conversion of gas pollutants in the atmosphere. In this study, the effects of combustion conditions (the fuel/oxygen ratio and sulfur in fuel) on the composition, morphology and hydrophilicity of soot have been investigated. The heterogeneous reaction of SO2, O3 and NO2 with soot was investigated using in situ attenuated total internal reflection infrared (in situ ATR-IR) spectroscopy, ion chromatography (IC) and a flow tube reactor. The roles of relative humidity (RH) and the surface composition of soot in the reaction of SO2 with soot, the roles of OC and EC in the reactions of O3 with soot and the role of the microstructure of EC in the reaction of NO2 with soot were studied. The main contents and results are shown as follows: (1) Soot samples were prepared by combusting n-hexane under controlled conditions. The results showed that combustion conditions significantly affected the properties of soot. The content of unsaturated species in OC and the defect content of graphene in EC increased as a function of the fuel/oxygen ratio. Under lean fuel combustion conditions, the properties of flame soot were influenced remarkably by the sulfur content in the fuel. As the sulfur content increased, sulfate species in lean flame soot increased nonlinearly, while sulfate species on the surface of lean flame soot increased linearly. The hygroscopicity of lean flame soot from sulfur-containing fuel was greatly enhanced due to sulfate species on the surface of soot. Meanwhile, a high sulfur content in fuel was favorable for alkyne formation, leading to the increase in the diameter of the primary lean flame soot particles and the number concentrations of accumulation mode particles. (2) RH showed profound impacts on the heterogeneous reaction of SO2 with soot. In the RH range from 6% to 68%, water promoted SO2 adsorption and sulfate formation, while excessive water condensed on soot was unfavorable for sulfate formation due to inhibition of SO2 adsorption when RH was higher than 80%. The surface composition of soot, which was governed by combustion conditions, also played an important role in the heterogeneous reaction of SO2 with soot. This influence was found to greatly depend on RH. Appropriate amounts of water and SO2 adsorbed on soot were favorable for sulfate formation. At the low RH of 6%, soot prepared with the higher fuel/oxygen ratio of 0.162 exhibited a maximum uptake capacity for SO2 because it contained a large amount of aromatic C−H groups, which acted as active sites for SO2 adsorption. At the high RH of 54%, soot prepared with the lower fuel/oxygen ratio of 0.134 contained appropriate amounts of aromatic C−H groups and oxygen-containing groups, leading to the optimal surface concentrations of both SO2 and water. For soot prepared with the higher fuel/oxygen ratio of 0.162, aging by O3 led to an enhancement in the reactivity toward SO2 due to the decrease in the amounts of aromatic C−H groups and increase in the amounts of oxygen-containing groups. For soot prepared with the lower fuel/oxygen ratio of 0.134, aging by O3 decreased the reactivity toward SO2. (3) The reactivity of soot toward O3 was closely related to combustion conditions. As the fuel/oxygen ratio increased, the uptake coefficient of O3 on soot increased and correlated linearly with the content of unsaturated species in OC. The uptake coefficient of O3 on EC increased with the fuel/oxygen ratio and increased linearly with the defect content of graphene in EC. These results suggested that the reactivity of soot toward O3 was governed by the composition of OC and microstructure of EC. (4) The microstructure of EC, governed by the fuel/oxygen ratio, showed a significant effect on the reactivity of soot toward NO2. The uptake coefficient of NO2 and yield of HONO increased with the increase of fuel/oxygen ratio and depended linearly on the defect content of graphene in EC, suggesting that defects were the main active sites of EC toward NO2. Compared to prime EC, EC aged by O3 at room temperature and O2 at 300ºC exhibited a great decrease in NO2 uptake coefficient and HONO yield. However, oxidized EC showed a prominent enhancement in NO yield. The carbonyl oxygens of quinones formed on oxidized EC contributed to the conversion of NO2 to NO.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38753
Appears in Collections:大气污染控制中心_学位论文

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作者单位: 1.中国科学院生态环境研究中心

Recommended Citation:
赵燕. 典型大气污染物与黑碳的非均相反应研究[D]. 北京. 中国科学院大学. 2017.
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