基于外场观测的大气二次有机气溶胶研究

二次有机气溶胶（SOA）是指挥发性有机物在大气中发生光化学氧化进入到颗粒相的产物,由于其具有强烈的环境效应、气候效应和人体健康效应,因此成为大气化学研究的热点. 然而由于SOA的复杂性和测量技术的限制,目前对SOA的研究还非常有限. 总体来说,对SOA的研究手段主要有三种方法：实验室模拟、模式模拟和基于外场观测的SOA研究. 由于SOA的研究非常广泛,本文仅综述了基于外场观测的SOA组成、来源和生成机制的研究,重点在于SOA组分的测量和总量的估算. 基于外场观测的SOA研究是随着技术的发展而发展的,早期的研究仅仅能对SOA的少数物种进行测量,主要是一些有机酸和多羟基化合物;也有利用一些假设对SOA进行粗略的估算,如受体模型法、非生物质燃烧水溶性有机物法;随着SOA实验室模拟研究和示踪物测量技术的发展,二次有机示踪物法真正做到了对特定前体物VOC生成SOA的估算;随着在线测量技术的提高,EC示踪/CO示踪和OC/EC比值法和基于气溶胶质谱（AMS）-正交矩阵模型（PMF）的方法被广泛应用于SOA的估算. 尤其是AMS-PMF联用方法的出现为SOA来源和生成机制的研究开拓了新的方向. 对AMS技术和示踪物技术的进一步联合和开发有望成为未来SOA研究重要的方向.     

用气溶胶飞行时间质谱实时探测甲苯光氧化产生的单个二次有机气溶胶粒子

在烟雾腔内, 用紫外光照射甲苯、亚硝酸甲酯、一氧化氮和空气的混合物, 可以启动甲苯和羟基自由基(OH·)的光氧化反应和一系列的后续反应, 产生非挥发性和半挥发性有机化合物. 半挥发性有机化合物可以在气态和粒子态之间进行分配, 产生二次有机气溶胶粒子. 用自制的气溶胶飞行时间质谱仪, 快速、实时测量这些粒子的尺度、它们的分子成分和直径分布.     

二次有机气溶胶估算方法比较研究

为研究北京夏季二次有机气溶胶（SOA）浓度,比较多种SOA估算方法的不确定性和在我国的适用性,在CAREBEIJING 2008大型观测期间在城市点北大点和郊区点榆垡点采集大气颗粒物PM_2.5样品,利用多种方法对二次有机碳（SOC）的浓度进行了估算,估算方法包括二次有机示踪物产率法、非一次源OC法、非生物质燃烧水溶性有机碳法（WSOC）和元素碳示踪有机碳/元素碳比值法.估算结果表明,二次有机气溶胶已经成为北京颗粒有机物的重要组成部分,夏季SOC可以占总有机碳（OC）的50%甚至更高。通过模拟我国典型的生物质燃烧,实测建立适合我国的获得了非生物质燃烧WSOC方法中的重要参数,即获得方法中重要参数生物质燃烧排放颗粒物中WSOC/OC的比值,我国生物质燃烧颗粒物中该比值平均为0.48±0.04.多种方法结果均表明,SOA已经成为北京颗粒有机物的重要组成部分,所占比例可以达到50%甚至更高.利用化学质量守恒模型（CMB）和示踪物产率法对颗粒有机物来源进行闭合发现,依靠目前的示踪物技术北京大气颗粒有机物中仍然有20%～27%的来源不清楚.通过综合比较了多种SOC估算方法,确定了各方法在我国的适用性： 示踪物产率法、非一次源OC法和EC示踪OC/EC比值法可适用于我国大气中SOC的估算,但是非生物质燃烧WSOC方法仅适用于我国大气中水溶性SOC的估算,但是不同方法之间存在的系统误差.本研究还对这几种方法的不确定性做了初步的分析,为其他研究者选择估算方法提供参考和依据.示踪物产率法仅估算了几种特定VOCs前体物对SOC贡献,因此低估了总的SOC,但是这种方法是目前唯一一种可以估算特定VOCs前体物对SOC贡献的方法;同样地,非生物质燃烧WSOC法仅估算了水溶性的SOC,因此也低估了总的SOC;非一次源OC法高估了SOC,这主要是由于未能解析出的一次源OC造成的.而且这种高估在城市地区更为显著,主要是因为城市地区一次源相对比较复杂造成的;非生物质燃烧WSOC法低估了总的SOC,而且这种方法仅适用于我国水溶性SOC的估算;EC示踪OC/EC比值法的主要不确定性来自于一次源OC/EC比值的确定,由于这个比值造成的单点误差最高可高估54%或低估64%.     

基于高分辨质谱在线观测的2011深圳大运会前后PM_1化学组成与粒径分布

本文利用先进的高分辨飞行时间气溶胶质谱仪（HR-ToF-AMS）于2011年深圳世界大学生运动会前后（2011年8月3日~9月22日）对深圳市区大气亚微米细粒子（PM1）化学成分和粒径分布进行了在线测量.结果表明,整个观测期间PM1质量浓度平均为51.1±32.6gm3,其中有机物占颗粒物总质量的37.9%,硫酸盐为37.1%,铵盐11.9%,黑碳6.6%（由一台单颗粒黑碳光度计（SP2）单独测量）,硝酸盐5.8%,氯化物0.6%.观测期间各成分（除黑碳外）的粒径分布峰值位于真空动力学粒径550nm附近,而有机物在较小粒径范围（100~200nm）仍有较多质量分布,显示出本地一次源的明显贡献.基于高分辨有机质谱计算得到的有机气溶胶的平均元素组成为：碳34.0%、氢53.2%、氧12.0%和氮0.8%（原子个数百分比）,对应的OM/OC（有机物与有机碳质量比）平均值为1.66±0.16.采用正矩阵因子解析（PMF）模型对有机气溶胶高分辨质谱进行因子解析,得到三类有机气溶胶：HOA（还原态有机气溶胶）,SV-OOA（半挥发氧化态有机气溶胶）和LV-OOA（低挥发氧化态有机气溶胶）,分别占有机物总量的31.3%,39.8%和28.9%,说明二次有机气溶胶（以SV-OOA和LV-OOA之和代表）是有机气溶胶的主体部分.结合气团来源分析不同时段PM1化学组成和粒径分布特征表明,大运会召开期间PM1质量浓度水平比整个观测期间的平均值低60.7%,是气团来自洋面等有利气象条件和黄标车限行等污染源控制措施的综合作用结果.     

二次有机气溶胶形成的化学过程

挥发性有机化合物的光氧化过程和光氧化产物的气态/粒子态均分过程是二次有机气溶胶形成的重要原因.二次有机气溶胶形成的化学机理主要涉及到挥发性有机化合物的光氧化过程及其一系列的后续反应,它们导致了对流层中臭氧浓度的增加和二次有机气溶胶的形成.本文将重点介绍二次有机气溶胶形成的重要化学过程和量子化学计算研究.     

二次有机气溶胶的水相形成研究

二次有机气溶胶是大气颗粒物中的主要成分,对大气环境、气候以及人类健康等有重要影响。近年来的研究表明,水相形成二次有机气溶胶与传统气相形成二次有机气溶胶对二次有机气溶胶的贡献相当,且能够解释用传统气相形成方法无法解释的野外观测与模型模拟以及野外观测与室内烟雾箱模拟二次有机气溶胶在颗粒大小、分布、浓度以及老化程度等方面的差异,因而成为研究的热点。本综述重点介绍了目前大气中二次有机气溶胶水相形成的实验室研究,包括黑暗条件下的非自由基反应(水合、缩醛/半缩醛、醇醛缩合和催化反应)和光照条件下的自由基反应。同时,对二次有机气溶胶水相形成研究的发展方向进行了展望。     

苯乙烯-NOx光照的二次有机气溶胶生成

在烟雾箱内研究了温度为(301±2) K时苯乙烯-NO_x-air光照体系生成的二次有机气溶胶(SOA). 分别探讨了高相对湿度(RH＝72%)对SOA的化学组分、数浓度、产率等的影响. 通过长光程傅立叶红外(FTIR)得到苯乙烯-NO_x光照体系的气相产物主要有甲醛、苯甲醛、甲酸和CO等. 采用聚四氟乙烯(PTFE)膜对SOA进行富集, 用FTIR对其化学组分进行分析, 推得SOA的主要物种有过氧苯甲酸硝酸酯、苯甲酸羟基苯基甲酯和苯甲酸. 高相对湿度时气相产物中甲酸量显著提高, 同时SOA红外谱图中新增加了苯甲酸, 而酯中的羰基吸收峰却比低相对湿度时降低了, 从而证实了H₂O与Criegee双自由基反应生成苯甲酸的路径, 同时也间接地说明了Criegee双自由基与苯甲醛反应生成苯甲酸羟基苯基甲酯的存在. 高相对湿度时SOA的数浓度比低相对湿度时降低了约36%～44%, 但根据在膜上的SOA质量得到高相对湿度时SOA产率比低相对湿度时提高了约40%, 说明高相对湿度增大了SOA的粒子尺度.     

二次有机气溶胶的气体/粒子分配理论

本文重点评述了二次有机气溶胶形成的气体/粒子分配理论,简要介绍了它的发展和可能的应用.在大气中,气体有机物种的氧化可以产生半挥发性的有机化合物,二次有机气溶胶的形成可以用气体/粒子分配的吸收模型来评估.气体/粒子分配过程决定于半挥发性化合物的成分、浓度和蒸气压,以及吸收性材料的浓度和成分.在气体/粒子分配理论的基础上,人们又研究和开发出二次有机气溶胶的分子组分的气体/粒子分配的热力学模型,它可以用来预估气溶胶中液态水的含量、无机物的分布、亲水性和疏水性有机物的分布.二次有机气溶胶形成的化学机理和气体/粒子分配的热力学模型与加利福尼亚工学院三维都市/区域性大气模型相结合,可以用于气相和气溶胶相模拟.     

硫酸钙及硫酸铵气溶胶对二次有机气溶胶生成的影响

二次有机气溶胶(SOA)是大气光化学反应的产物, 也是城市和郊区大气中细粒子的主要成分. 本研究致力于考察高浓度无机气溶胶颗粒对SOA生成的影响. 实验系统采用2 m³的温控烟雾箱, 以干燥的CaSO₄和(NH₄)₂SO₄为无机种子气溶胶, 研究了间二甲苯/NO_x/空气体系光氧化生成SOA的过程. 实验结果显示间二甲苯和NO_x在紫外光照下会产生大量SOA, SOA产率可用单产物模型表征. CaSO₄气溶胶的存在对SOA产率曲线没有明显的影响, 而(NH₄)₂SO₄气溶胶的存在使气相半挥发性氧化产物的生成量增加36%, 显著地增加了SOA的产率. (NH₄)₂SO₄粒子在含水有机物作用下显现的弱酸性可能是导致这一影响的主要原因. 该实验结果有助于更详尽地阐明中国颗粒物污染严重城市SOA的生成机理, 从而为进一步修正空气质量模型提供依据.     

基于实验室模拟研究二次有机气溶胶生成及老化机制

由于二次有机气溶胶(SOA)对气候变化、区域污染和人体健康具有明显的影响,因此受到了广泛的关注.基于实验室的方法可以在稳定可控的条件下探讨SOA的生成机制,其中环境烟雾箱和气溶胶生成潜势反应器是最常用的两种模拟工具.本文综述了基于这两种模拟工具对SOA产率的影响因素、SOA生成机制和SOA老化过程中性质演变特征的研究.影响SOA产率的因素主要包括OH暴露量,NO_x水平(VOCs/NO_x),种子颗粒物的浓度及种子颗粒物的化学组成. SOA产率随着OH暴露量、VOCs/NO_x比值的增加均先增后减;种子颗粒物的存在会通过提高气态中间产物的凝结汇,从而促进物质从气相到颗粒相的转化;酸性种子颗粒物可以通过提高摄取系数并提供酸催化条件促进SOA的生成;种子颗粒物中的金属离子和矿物质也会通过催化作用或者影响氧化剂的产生等过程对SOA的生成和老化产生作用.本综述还总结了不同源排放气态前体物SOA的生成潜势以及生成SOA的特征.等效光氧化龄约为2～3 d时,汽油发动机排放生成SOA量达到最高值,增长倍数(SOA/POA, POA即为一次有...     

Real-time detection of individual secondary organic aerosol particle from photooxidation of toluene using aerosol time of flight mass spectrometer

Aromatic hydrocarbons are air pollutants in urban atmosphere and mainly from anthropogenic sources, i.e., emission from automotive exhaust and productive process of industry, and they constitute an important fraction of total volatile organic compounds (VOCs). Photochemical ozone and secondary organic aerosols (SOA) could be formed from the photochemical proc- esses of aromatic hydrocarbons. SOA may impact visibility of air, formation of clouds, change of the climate, and human health serio…     

Identification of secondary organic aerosols based on aerosol mass spectrometry

Secondary organic aerosol (SOA) is one of the major components of aerosols in the atmosphere and has not been well understood so far. Due to the complex chemical composition of organic aerosols, the identification of SOA has been a hotspot and difficult issue in the field of aerosol study. This study attempts to quantitatively identify SOA in winter of Shenzhen based on positive matrix factorization (PMF) analysis. Major sources were resolved and SOA was identified subsequently according to the characteristic ion fragments measured by highly time-resolved aerosol mass spectrometer measurement. It showed that in the winter of Shenzhen the average SOA concentration was 9.41 ± 6.33 μg/m³, accounting for 39.9 ± 21.8% of the total organic mass. Compared with primary organic aerosol (POA), the SOA concentrations had no large variation, suggestive of characteristics of regional secondary pollutants. The ratio of SOA/BC had pronounced diurnal variation, similar to that of O _x (O₃+NO₂), indicating SOA formation was significantly controlled by activity of photochemistry in the atmosphere. The most effective period for SOA formation was from 9 am ～3 pm since the SOA/BC ratio increased by 122% during this period. This study provides a new technical method and a new idea for SOA investigation.     

Characterization of 2-methylglyceric acid oligomers in secondary organic aerosol formed from the photooxidation of isoprene using trimethylsilylation and gas chromatography/ion trap mass spectrometry

In the present work, we have characterized in detail the chemical structures of secondary organic aerosol (SOA) components that were generated in a smog chamber and result from the photooxidation of isoprene under high-NO(x) conditions typical for a polluted atmosphere. Isoprene high-NO(x) SOA contains 2-methylglyceric acid (2-MG) and oligoester derivatives thereof. Trimethylsilylation, in combination with capillary gas chromatography (GC)/ion trap mass spectrometry (MS) and detailed interpretation of the MS data, allowed structural characterization the polar oxygenated compounds present in isoprene SOA up to 2-MG trimers. GC separation was achieved between 2-MG linear and branched dimers or trimers, as well as between the 2-MG linear dimer and isomeric mono-acetate derivatives thereof. The electron ionization (EI) spectra of the trimethylsilyl derivatives contain a wealth of structural information, including information about the molecular weight (MW), oligoester linkages, terminal carboxylic and hydroxymethyl groups, and esterification sites. Only part of this information can be achieved with a soft ionization technique such as electrospray (ESI) in combination with collision-induced dissociation (CID). The methane chemical ionization (CI) data were used to obtain supporting MW information. Interesting EI spectral differences were observed between the trimethylsilyl derivatives of 2-MG linear and branched dimers or trimers and between 2-MG linear dimer mono-acetate isomers.     

Comparative study of organic dyes with time-of-flight static secondary ion mass spectrometry and related techniques

A series of cationic, zwitterionic and anionic fluorinated carbocyanine dyes, spin-coated on Si substrates, were measured with time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) under Ga(+) primary ion bombardment. Detailed fragmentation patterns were developed for all dyes measured. In the positive mode, the resulting spectra showed very intense signals for the precursor ions of the cationic dyes, whereas the protonated signals of the anionic dyes were hardly detected. Differences of three orders of magnitude were repeatedly observed for the secondary ion signal intensities of cationic and anionic dyes, respectively. All measured dyes yielded mass spectra containing several characteristic fragment ions. Although the secondary ion yields were still higher for the cationic than the anionic dye fragments, the difference was reduced to a factor of < or =10. This result and the fact that M(+), [M + H](+) or [M + 2H](+) are even-electron species make it very likely that the recorded fragments were not formed directly out of the (protonated) parent ions M(+), [M + H](+) or [M + 2H](+). In the negative mode, none of the recorded spectra contained molecular information. Only signals originating from some characteristic elements of the molecules (F, Cl), the anionic counter ion signal and some low-mass organic ions were detected. A comparative study was made between TOF-S-SIMS, using Ga(+) primary ions, and other mass spectrometric techniques, namely fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). The measurements showed that MALDI, ESI and FAB all give rise to spectra containing molecular ion signals. ESI and FAB produced M(+) and [M + H](+) signals, originating from the cationic and zwitterionic dyes, in the positive mode and M(-) and [M - H](-) signals of the anionic and zwitterionic dyes in the negative mode. With MALDI, molecular ion signals were measured in both modes for all the dyes. Structural fragment ions were detected for FAB, ESI and MALDI in both the positive and negative modes. Compared with the other techniques, TOF-S-SIMS induced a higher degree of fragmentation.     

Experimental study on synchrotron radiation photoionization of secondary organic aerosol derived from styrene ozonolysis

Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on-line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off-line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV-PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off-line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles.     

Determination of oxygenated compounds in secondary organic aerosol from isoprene and toluene smog chamber experiments

The determination of multifunctional oxygenated compounds in secondary organic aerosols (SOA) usually requires a derivatisation protocol prior to gas chromatography-mass spectrometry analysis (GC-MS). Our proposed protocol, a combination of O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) plus diluted N-methyl-N-trimethyl-silyltrifluoroacetamide (MSTFA) without catalyst, has improved the determination of carbonyls, polyhydroxyl-compounds, hydroxyl-carbonyls, hydroxyl-carboxylic acids and di-carboxylic acids. The optimised derivatisation protocol has been successfully used for blanks, standard mixtures and photo-oxidation products from isoprene and toluene generated in a high-volume simulation chamber (European Photoreactor, EUPHORE).

Some previously identified degradation products for isoprene including tetrols such as threitol, erythritol; 2-methyltetrols and 2-methylglyceric acid; and for toluene including nitrophenols, methyl-nitrophenols, benzaldehyde, p-cresol, benzoic acid, glyoxylic acid and methyl-glyoxylic acid, have been identified in our aerosol samples, thus confirming the successful applicability of the proposed derivatisation protocol. Moreover, the reduction of artefacts and enhanced signal-to-noise ratio, have allowed us to extend the number of multifunctional compounds determined. These findings have demonstrated the validity of this analytical strategy, which will contribute to a better understanding of the atmospheric degradation chemistry of biogenic and anthropogenic pollutants.     

A two-point calibration method for quantifying organic binary mixtures using secondary ion mass spectrometry in the presence of matrix effects

Quantification of the composition of binary mixtures in secondary ion mass spectrometry (SIMS) is required in the analyses of technological materials from organic electronics to drug delivery systems. In some instances, it is found that there is a linear dependence between the composition, expressed as a ratio of component volumes, and the secondary ion intensities, expressed as a ratio of intensities of ions from each component. However, this ideal relationship fails in the presence of matrix effects and linearity is observed only over small compositional ranges, particularly in the dilute limits. In this paper, we assess an empirical method, which introduces a power law dependence between the intensity ratio and the volume fraction ratio. A previously published physical model of the organic matrix effect is employed to test the limits of the method and a mixed system of 3,3′-bis(9-carbazolyl) biphenyl and tris(2-phenylpyridinato)iridium (III) is used to demonstrate the method. This paper introduces a two-point calibration, which determines both the exponent in the power law and the sensitivity factor for the conversion of ion intensity ratio into volume fraction ratio. We demonstrate that this provides significantly improved accuracy, compared with a one-point calibration, over a wide compositional range in SIMS quantification and with a weak dependence on matrix effects. Because the method enables the use of clearly identifiable secondary ions for quantitative purposes and mitigates commonly observed matrix effects in organic materials, the two-point calibration method could be of significant benefit to SIMS analysts.     

有机化学反应中间体的质谱分析

有机化学反应中活性中间体的性质各异,对反应中间体的表征和研究对于阐明和确证反应机理、优化反应条件、筛选催化剂和发现新类型反应至关重要.近年来,质谱技术和在线微量采样技术的发展,极大程度地拓展了质谱学在该领域的应用.本文总结了近年来本领域发展的新策略、技术和方法,以及有机质谱技术在反应中间体研究中的应用.     

Ultraviolet photocatalytic degradation of cholesterol on TiO2: secondary ion mass spectrometry

Cholesterol (C₂₇H₄₆O stated as M) is used as a model of bio‐organic contamination, because this compound is in almost every living organism, and its photocatalytic degradation on titanium oxide (TiO₂) surface with UV exposure is investigated. Secondary ion mass spectrometry as a surface‐sensitive technique is suited to study this degradation process with focus on intermediates. A fragment of M–OH represents the intact molecule of cholesterol and provides its relative concentration on the surface. The intensity of M–OH decreases after 24‐h UV irradiation, and the level of degradation is 89% with the pseudo‐first kinetic constant of 0.0207 min^?1 within 2 h. A fragment of MO–H represents an intermediate as one of the cholesterol oxidation products. The irradiation from a bottom in comparison with a top reveals the differences in the mechanism of the intermediate formation through the intensity and the kinetics with values of factor of 1/3 and 30 min, respectively. The roles of electrons and holes, primarily generated in TiO₂ by UV, and also of superoxide anion radical and hydroxyl radical, as the secondary reactive species, are discussed to illustrate the bottom/top mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.