Category Archives: 科研进展

ES&T: 我国大气中非经意产生的多氯联苯(UP-PCBs)

赵时真 博士后

氯联苯(PCBs)是首批列入斯德哥尔摩公约的有机污染物之一,虽全球禁用多年,但近年环境浓度下降缓慢,在包括我国在内的一些地区甚至出现反弹。究其原因,可能是过去大部分研究通常只关注工业生产的多氯联苯(Aroclor PCBs),而忽略了工业热过程、燃烧活动等非经意产生的多氯联苯(UP-PCBs)在环境中的污染水平和对人群的潜在风险。近年来,非工业生产的多氯联苯(non-Aroclor PCBs),在欧美国家的大气、土壤、沉积物和人体血清等不同介质中被广泛检出。在我国,少量相关研究仅局限于个别单体和个别污染源的发现上,关于这些污染物的污染特征、排放格局及其在区域环境上的影响还知之甚少。

近日,中国科学院广州地球化学研究所赵时真博士、张干研究员与英国Lancaster大学Kevin Jones、Andy Sweetman等合作,采用大气被动采样(PUF-PAS)的方法,对我国55个站点进行了为期3个季度(2016-2017)的野外观测,采样点覆盖特征PCBs源点、城市点、郊区点和偏远点。通过对大量样品中209种PCBs单体的高通量定量分析,结合同步特征源谱解析,对我国大气中不同来源PCBs的贡献进行了精准识别和定量评估。研究发现,UP-PCBs已经成为我国大气中PCBs的主要来源,对大气PCBs问题的贡献超过60%,主要来自有机颜料生产和热工业及燃烧活动。虽然如此,电子垃圾来源的PCBs对于工业品Aroclor PCBs的贡献仍过半,不容忽视。UP-PCBs来源复杂、控制难度大,该研究结果为相关部门制定合理的管控措施提供了科学参考。

该研究得到了国家重点研发项目(2017YFC0212004)、广东省“珠江人才计划”本土创新科研团队项目(2017BT01Z134)和中国博士后科学基金(2017M622814,2018T110898)的联合资助。相关成果发表在国际期刊Environmental Science & Technology上,并遴选为当期Supplementary cover。

论文信息:Zhao, S., Jones, K.C., Li, J., Sweetman, A.J., Liu, X., Xu, Y., Wang, Y., Lin, T., Mao, S., Li, K., Tang, J. and Zhang, G.* (2020) Evidence for Major Contributions of Unintentionally Produced PCBs in the Air of China: Implications for the National Source Inventory. Environmental Science & Technology 54(4), 2163-2171.

全文链接:https://pubs.acs.org/doi/10.1021/acs.est.9b06051

图1 ES&T Supplementary cover

图2 正定矩阵因子分析模型(PMF)解析我国城市大气中PCBs的主要源谱

图3 不同来源PCBs对我国大气中总PCBs的相对贡献

JGR-A: Photochemical formation of unsaturated multifunctional and organosulfur compounds at air‐water interface

Sasho 研究员

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous at the sea surface. Dimethyl sulfoxide (DMSO) represents the most abundant organic sulfur compound in the oceans. Decades of research on the photodegradation of polycyclic aromatic hydrocarbons (PAHs) have provided fundamental and practical insights into these processes; however, the structure of many organic compounds formed during the photodegradation and the reaction pathways leading to their formation still remain unclear. This study provides an experimental evidence that PAHS, such as fluorene (FL) dissolved in DMSO, when exposed to sunlight, can initiate photosensitized chemistry at the air-water interface into highly oxygenated and toxic unsaturated multifunctional compounds which are known precursors of secondary organic aerosols (SOA). The photosensitized properties of excited triplet state (3FL*) and its reactivity have been investigated using transient spectroscopy with a laser flash photolysis. From the reaction between DMSO and 3FL*, the formation of organosulfur compounds (OS) was observed in both the aqueous phase and gas phase. Some of the organosulfur compounds identified here exhibit the same molecular composition with the organosulfur compounds detected in ambient aerosols, highlighting the importance of the photosensitized reactions of PAHs at the water surface.

We determine the generated liquid-phase and gas phase products by means of two state-of-the-art, ultrahigh-resolution mass spectrometric instruments: Ultrahigh-Resolution Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS) and Ultrahigh-Resolution Hybrid Quadrupole Orbitrap Mass Spectrometer which was interfaced with a secondary electrospray ionization source (SESI-HRMS).

From the detected products in the gas phase and in the aqueous phase we propose a detailed reaction pathways for the photosensitized degradation of FL. The experimental results are supported by quantum-mechanical calculations using density functional theory (DFT) by the Gaussian 03 suite of programs.

The photosensitized chemistry suggested in this study may exert a very large impact, especially if in general the mere presence of a surface layer of PAHs can trigger this interfacial photosensitized chemistry at sea surface, cloud droplet, and the surface of aerosol deliquescent particles. Because PAHs-covered water surfaces are ubiquitous, the formation of unsaturated multifunctional compounds and OS compounds might also influence the formation of SOA in the atmosphere, which in turn can better explain field observations of new particle formation events which are occurring independently of the primary emitted particles from marine biological activity.

The van Krevelen graph for CcHhOo group of compounds, formed upon 4 hr of light irradiation of FL/DMSO and detected in ESI− mode. The recognized repeating mass building increments are labeled in the legend. All other molecules which do not participate in any building block increments are depicted in black color. A and B areas depict oxygenated aliphatic compounds and low‐oxygenated aromatic hydrocarbons, respectively. The aromaticity equivalent (black with Xc < 2.5, red with 2.5 ≤ Xc < 2.7, and green with Xc ≥ 2.7) is illustrated by the color bar, while the pie chart demonstrates the percentage value of each color‐coded compound in the sample.

Detailed reaction mechanism describing the formation of gas phase products initiated by 3FL*. Numbers in brackets, written below each molecule, present compound designations to follow the discussion better with the Scheme 2. All identified products are framed into red rectangles

The result was published in JGR-Atmosphere, recently.

Majda Mekic Jiafa Zeng Bin Jiang Xue Li Yannis G. Lazarou Marcello Brigante Hartmut Herrmann Sasho Gligorovski. Formation of Toxic Unsaturated Multifunctional and Organosulfur Compounds From the Photosensitized Processing of Fluorene and DMSO at the Air‐Water Interface. Journal of Geophysical Research: Atmospheres125, e2019JD031839.

URL: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019JD031839

ACP: 典型源排放颗粒物中棕色碳的光学性质与有机分子组成

唐娇 博士研究生

棕色碳(BrC)是一类在近紫外和可见光区吸收光辐射的有机碳,不仅对大气造成辐射强迫,更是对大气光化学反应速率有着重要作用。棕色碳的结构复杂、种类众多以及来源广泛。大量的研究表明生物质燃烧、煤燃烧、机动车尾气、生物排放以及二次有机气溶胶等是BrC的重要来源。但是,不同源排放的BrC进入大气后,受到复杂的大气化学过程,其光学性质和化学结构会发生很大的变化,这增加了研究BrC的难度,尤其是BrC的源解析。因此,从源头研究BrC是了解BrC大气演化的一个重要前提条件。
中国科学院广州地球化学研究所有机地球化学国家重点实验室的博士研究生唐娇、李军研究员、张干研究员等,与复旦大学陈颖军教授、中国科学院烟台海岸带研究所的唐建辉研究员等合作,选择模拟生物质开放燃烧和家用煤燃烧,以及机动车尾气等典型源排放的大气颗粒物中的溶解性BrC为研究对象,基于激发-发射荧光技术(EEM)-平行因子分析(PARAFAC)和傅里叶变换离子回旋共振质谱(FT-ICR-MS)等技术,对其光学和分子组成进行了较系统的解析。研究结果表明,不同源样品的不同溶解组分分别具有独特的荧光成分组成特征(图1和图2),这种独特的荧光成分组成特征可能受到其分子组成结构特征的影响(图3)。典型源排放样品中溶解性棕色碳的吸光能力,主要受分子质量和不饱和度影响(图4)。该研究对棕色碳的光学、结构及分子进行了详细探究,为进一步了解BrC在大气中的演化及其源解析,提供了重要实验依据。

图1. 平行因子识别的生物质开放燃烧、家用煤燃烧和机动车排放样品的水溶性有机碳(WSOC,P1-6)和甲醇溶的有机碳(MSOC,C1-6)组分中的荧光成分图

图2. 平行因子识别的生物质开放燃烧、家用煤燃烧和机动车排放样品的水溶性有机碳(WSOC,a)和甲醇溶的有机碳(MSOC,b)组分中的相对荧光成分的贡献

图3. 维恩图(Venn diagram)识别的生物质开放燃烧、家用煤燃烧和机动车排放样品的水溶性有机碳(WSOC,a)和甲醇溶的有机碳(MSOC,b)中独立分子化合物的范式图(Van Krevelen)分布

图4. 可能BrC分子的等效双键指数(DBE)和分子质量(MW)与水溶性有机碳(WSOC,a)和甲醇溶的有机碳(MSOC,b)组分的吸光能力(MAE365)之间的线性关系

此项研究成果,近期发表在国际期刊Atmospheric Chemistry and Physics上。

论文信息:Tang, Jiao; Li, Jun; Su, Tao; Han, Yong; Mo, Yangzhi; Jiang, Hongxing; Cui, Min; Jiang, Bin; Chen, Yingjun; Tang, Jianhui; Song, Jianzhong; Peng, Ping’an; Zhang, Gan. Molecular compositions and optical properties of dissolved brown carbon in biomass burning, coal combustion, and vehicle emission aerosols illuminated by excitation-emission matrix spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry analysis. ATMOSPHERIC CHEMISTRY AND PHYSICS, 2020, 20(4): 2513-2532. DOI: 10.5194/acp-20-2513-2020
相关链接:https://www.atmos-chem-phys.net/20/2513/2020/