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华北平原冬夏季大气H2O2的污染特征、来源以及环境影响研究
Alternative TitleStudy on the Pollution Characteristics, Sources and Environmental Impact of Atmospheric H2O2 in Summer and Winter of the North China Plain
叶灿
Subtype博士
Thesis Advisor牟玉静
2020-05
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境科学
Keyword过氧化氢 硫酸盐, Fe-hulis复合物 ,臭氧敏感性
Abstract

       对流层大气中过氧化氢(H2O2)主要来源于挥发性有机物 VOCs)和一氧化碳( CO)光氧化产生的 过氧 氢氧自由基( HO2)自身耦合反应,是终止大气中奇氢自由基( OH和 HO2)所引发大气化学反应的主要通道之一,对光化学臭氧O3)、硝酸盐、硫酸盐以及二次有机气溶胶等形成具有显著影响。此外 H2O2是大气中 一种 重要的氧化剂, 对植被和人体健康具有显著危害,且 在液相中能够氧化 SO2促进硫酸盐的形成 等。 目前国内 关于大气中 H2O2的观测研究相对薄弱,且主要集中在夏季,从而局限了人们对我国大气污染特别是华北冬季严重灰霾成因的全面深入认识。为此,本文选择了华北典型城市和农村为主要研究对象,采用双通道酶促荧光法 H2O2分析仪以及多种气态和颗粒态污染物监测分析仪器,分别在北京市( 2016年 1月至 3月 )、河北省望都县东白陀村 2017年 11月至2018年 1月 以及 2016年 7月 至 8月 )以及山东省泰安市 2018年 5月至 7月共开展四次大型的外场观测 ,分析获得了三个典型地区大气中 H2O2的浓度水平、变化特征以及与其它污染物之间的关联性;估算了北京市冬季颗粒物 中 不同液相氧化通道对硫酸盐产率的贡献 ; 基于后向轨迹模型、气相盒子模型以及 多相模型的模拟研究,阐明了农村和泰安市大气 H2O2的主要来源和去除途径等。 取得的主要研究成果如下:
     1. 获得了 北京市和河北农村冬季 大气中 H2O2的浓度水平和变化特征, 发现两地冬季大气中均存在异常高浓度的 H2O2,提出该区域硫酸盐的 生成 机制以H2O2与 SO2在颗粒物液膜中的反应通道为主导,而不是最近研究提出的 NO2与 SO2液相反应通道。观测期间, 北京市和河北农村冬季大气中 H2O2在早上均随着太阳辐射强度增加而显著抬升,并在下午 14 00左右出现一个峰值,平均峰值浓度分别为 0.2 ppb和 0.45 ppb,最大小时平均浓度可高达 1.0 ppb 比最近文献假定值( 0.01 ppb)高 1-2个数量级。 河北农村冬季大气中H2O2在出现峰值后迅速下降,在 21 00左右降低到仪器检测限范围( 0.05 ppb),而 北京市 大气中 H2O2在 16 00-21 00又出现明显抬 升 ,然后缓慢下降,且整个夜间都维持在 0.12 ppb以上。
     2. 阐明了 北京市和河北农村冬季大气中 H2O2的主要来源。两地早上 H2O2的显著抬升通常伴随着几十个 ppb的高浓度 NO,大气中 HO2自由基由于可被高浓度NO快速消耗, HO2自由基 自身气相耦合反应通道无法解释 H2O2显著抬升 现象。进一步 分析 研究 发现 H2O2的 日间峰值浓度 与 PM2.5的平均浓度呈现正相关,因此 推测, H2O2可能来自颗粒相的光化学过程 。 为此,我们采用
多相模型 SPACCIM对 河北农村冬季大气中 H2O2进行了模拟研究,发现在未引入过渡重金属与腐殖酸耦合机制( Fe-HULIS)情况下,模型模拟 的 H2O2浓度远远低于实测值, 而引入后, 模型模拟 结果与观测值具有高度吻合性。河北农村地区由于冬季燃煤取暖,大气颗粒物中存在较高浓度的 过渡重 金属和腐殖酸, 颗粒相 中 Fe(Ⅲ)-HULIS的光解促进了 HO2自由基的产生, HO2自由基与 Cu+的多相反应最终促使 H2O2的产生 。此外,北京市冬季夜间 H2O2的显著抬升无法归咎于夜间大气化学反应贡献,因为夜间 O3和 NO3浓度由于高浓度 NO滴定作用通常接近零。我们采用后向轨迹模型分析发现, 北京市冬季 晚间 H2O2主要来自南部广大农村区域气团的输送。北京市处于燕山以及太行山形成的封闭地形内,位于传输廊道上容易受到南部传输的影响。
      3. 获得了河北农村 和山东泰安市夏季大气中 H2O2的 浓度水平和变化 特征 ,并初步探究了 H2O2的源汇机制。河北农村和山东泰安市夏季大气中 H2O2的浓度均呈现早晚浓度低而中午浓度高的显著日变化特征,浓度范围分别为 0-7.77 ppb和 0-6.06 ppb,平均值分别为 0.69 ppb和 0.93 ppb,与国内外报道的夏季 H2O2的浓度相比处于相对较高水平。 NOx是影响两地夏季 H2O2的 浓度重要因素,早上 H2O2的浓度只有当 NO降至 1 ppb左右时才出现明显抬升,表明 H2O2主要来自大气均相光化学过程。此外,河北农村观测到的一次异常高 H2O2浓度( 7.77 ppb)与 附 近 农田小麦 失火事件巧合, 通过卫星火点以及后向轨迹分析 表明生物质燃烧可能是 H2O2的一种重要来源。再有,河北农村大气中 H2O2以及 O3的浓度在小麦收割后集中施肥期间也出现明显抬升,推测施肥农田排放大量的 HONO,促进了区域光化学反应,导致了 H2O2和 O3的升高。 基于 泰安夏季 综合 观测 数据,采用 气相盒子模型 初步研究了H2O2的源汇机制。研究发现, 盒子模型中 H2O2干沉降速率 的默认值( 1 cm/s被严重低估了,导致 H2O2的模拟浓度显著高于实测值。而利用实测 H2O2浓度在 日间 的一级衰减曲线 估算 获得的 H2O2干沉降速率 约为 3 cm/s)),模拟值与实测值吻合 较好 。气相盒子模型结果显示 HO2自由基的双分子结合是夏季H2O2的主要来源通道,其次是 O3与烯烃的反应。 H2O2的 主要消耗的通道是干沉降,占到总消耗量的 84%,其次 是其 与 OH自由基的反应( 11%)以及自身光解( 5%)。 相对增量活性模拟结果 显示烯烃的削减对 H2O2浓度的影响最为明显,其次为芳香烃、甲醛、烷烃和乙醛。
      4. 诊断获得了 山东泰安市夏季大气中 O3形成的敏感化学区域。基于综合观测资料,分别采用 VOCs/NOx、 H2O2/NOz对 山东泰安市夏季大气中 O3形成的敏感化学区域 进行了诊断研究,发现多种诊断方法所获结果能够相互印证,均表明该市大气 O3形成 属于 VOCs和 NOx共同控制,且偏向 NOx控制。

Other Abstract

      H2O2 is mainly produced by the recombination of HO2 radicals, which  origin from the oxidation of volatile organic compounds (VOCs) and CO in the atmosphere. H2O2 production is one of the terminal reactions of HOx radicals, which has a significant impact on ozone, nitrate and sulfate formation. In addition, it is one of the most important oxidants in the atmosphere. H2O2 can oxidize SO2 in the aqueous phase leading to the formation of sulfate. Ground-level H2O2 exposure harms human and plant health. However, the field measurements about H2O2 are still sparse and mainly concentrate in summer season, which hinders deep understanding of its role in haze formation. In our study, H2O2 was measured based on dual-channel enzyme fluorescence method. Four comprehensive field experiments were carried out in the North China Plain. Winter field experiments included Beijing campaign (urban) from January to March 2016 and Wangdu campaign (rural) from November 2017 to January 2018. Summer field experiments included Wangdu campaign (rural) from July to August 2016 and Taian campaign (urban) from May to July 2018. The major findings in this study are as following:
     1. The field campaigns in Beijing and Wangdu demonstrated the levels of H2O2 and diurnal variations in two sites and found H2O2 oxidation rather than NO2 oxidation in aqueous-phase was the main pathway leading to the formation of sulfate during haze episodes. The winter H2O2 concentrations increased gradually with solar intensity increasing, reach maximum concentrations of 0.2 ppb and 0.45 ppb around 14:00 at the two sites, respectively. The maximum hourly-averaged H2O2 concentrations reached as high as 1 ppb, which was two magnitude higher than the modeled concentrations (0.01 ppb) by previous study.
     2. Our study has explored the sources of H2O2 during winter at the two sites. The steep increase of H2O2 during daytime in winter typically occurred with high NO concentrations, which would greatly suppress H2O2 production by the reaction of NO with HO2 radicals. Further analysis revealed that peak concentration of H2O2 was positively correlated with averaged PM2.5 levels during daytime, implying particle phase reactions may be responsible for the high H2O2 observed. We employed a multiphase model (SPACCIM) to study the potential multiphase H2O2 formation pathways. Without improvements, the initial modeling largely underestimated H2O2 concentrations. However, simulations with newly introduced Fe-HULIS chemistry shows a good agreement of modeled H2O2 concentrations with field data. Fe and HULIS were abundant in particles in rural areas in Hebei as they were frequent influenced by coal combustion and biomass burning events. The photolysis of Fe (Ⅲ)-HULIS promoted HO2 production and subsequent reaction with Cu+ would lead to H2O2 formation. Furthermore, evening peak of H2O2 in Beijing couldn’t attribute to photochemical reactions. Back-trajectory analysis showed that H2O2 in the evening was influenced by airmass transported from south areas with higher H2O2 concentrations. Beijing was surrounded by mountains on three sides and lies in the regional transport corridor of airmass.
     3. The summer field measurements demonstrated the levels and diurnal variations of H2O2 in Hebei and Taian. H2O2 in summer seasons exhibited typical diurnal pattern with low concentrations in the morning and evening and high concentrations in the afternoon. H2O2 concentrations in Taian and Wangdu ranged from 0-6.06 ppb with an average of 0.93 ppb and 0-7.77 ppb with an average of 0.69 ppb, respectively. Compared with the summer H2O2 concentrations reported in other studies, the levels in NCP were relatively high. H2O2 was low when NOx concentrations were high and started to increase until NOx decreased to nearly 1 ppb, indicating H2O2 was mainly produced in the gas-phase. There was a high H2O2 episode (7.77 ppb) observed in Wangdu summer campaign which was ascribed to biomass burning events by back-trajectory analysis and fire spots. Much higher H2O2 and O3 concentrations were observed after fertilization because the soil released high HONO and thereby promoted the photochemical reactions which accelerated the production of H2O2 and O3. We also employ a gas-phase box model to explore the source and sink of H2O2 in summer seasons. Initial modeling with dry deposition velocity of 1 cm/s largely overestimated H2O2 concentrations. When the dry deposition velocity calculated by first-order process was adopted, modeled and observed H2O2 matched very well. Simulations demonstrated that HO2 recombination was the main pathway leading to the formation of H2O2, followed by ozonolysis of alkenes. Dry deposition (84%) dominated the loss of H2O2, followed by the reaction of H2O2 with OH radicals (11%) and H2O2 photolysis (5%). RIR tests results suggested that reduction of alkenes lead to more pronounced decrease of H2O2, followed by aromatics, HCHO, alkanes and CH3CHO.
     4. The study has demonstrated the O3 formation regime in Taian city in summer. VOCs/NOx and H2O2 /NOz were employed to explore the O3 formation regime and all the results indicated that O3 was mainly formed in transition and NOx-limited regime.

Pages141
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/43691
Collection大气环境与污染控制实验室
Recommended Citation
GB/T 7714
叶灿. 华北平原冬夏季大气H2O2的污染特征、来源以及环境影响研究[D]. 北京. 中国科学院生态环境研究中心,2020.
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