Identification of missing organic reactivity in the urban troposphere

识别城市对流层中缺失的有机反应

• 批准号: NE/J008990/1
• 负责人: Dwayne Heard
• 金额: $ 23.6万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ008990%2F1
• 关键词: Identification; missing; organic; reactivity; urban

The international societal response to deteriorating air quality and the changing climate is guided by the predictions of numerical models. These models contain estimates of future emissions of trace gases and aerosols from natural and human activity, their dispersal throughout the atmosphere, and their chemical transformations into a wide range of secondary products. Photo-oxidation in the troposphere is highly complex, and is initiated by short lived radical species, in the daytime dominated by the hydroxyl radical, OH, and at night by either NO3 radicals or ozone. Chemical oxidation cycles remove primary emitted trace species which are directly harmful to humans (e.g. CO) or to the wider environment (greenhouse gases e.g. CH4,). However, many of the secondary products produced by atmospheric photo-oxidation are also directly harmful, for example O3, NO2, acidic and multifunctional species, many of which are of low volatility and are able to partition effectively to the condensed phase, creating secondary organic aerosol (SOA).In order to calculate the abundance of OH, and hence the lifetimes of other trace gases in the atmosphere, it is necessary to have fundamental knowledge of the rates of reaction of the processes that generate and remove OH. OH reacts with both organic and inorganic species, with the former generating significant uncertainty in any OH calculation, since many thousands of reactive volatile organic compounds (VOCs) exist in air. Practically, it has been impossible to identify all VOCs present in air and even where this has been attempted in a comprehensive manner, kinetic data on reaction rates are often missing. This complexity of VOCs, and limited associated data make it intrinsically difficult to reconcile observed OH concentrations and OH reactivity with model calculations. When attempted, significant mismatches are observed, highlighting some basic flaws in our ability to simulate the chemistry of the troposphere. Recent measurements of OH reactivity, combined with measurements of VOCs, have enabled the magnitude of missing OH sinks to be quantified, but not their chemical identity. Other measurements have shown that many unidentified organic components exist in ambient air when comprehensive two dimensional gas chromatography is used as the measurement technique.This proposal combines for the first time ultra high resolution VOC measurements developed by Lewis and Hamilton in York with the FAGE free-radical measurement and MCM modelling techniques developed by Heard, Whalley and Rickard in Leeds. We will determine the identity of missing organic material that contributes towards the removal of OH, and assess the formation of degradation products from their oxidation. This will be achieved by coupling comprehensive two-dimensional gas chromatography with a time-of-flight mass spectrometer and flame ionization detector with an OH chemical reactor. By exposing ambient air samples to a controlled environment containing enhanced OH radicals, and by observing the relative change of chromatographic peak intensity for unidentified species relative to the change in intensity for known VOC species (and for which the reactivity with OH is known) the OH reactivity of the unidentified species will be determined. The use a mass spectral detector will allow us to positively identify those species which we observe as contributing significantly as OH sinks, and, provide an assessment of the formation rates of secondary products formed. Using a functional group classification of the major species contributing to losses, we will create surrogate parameterized mechanisms for use in the MCM to allow a more accurate description of processes controlling urban OH and O3 Understanding the functionality of the missing reactivity will enable the atmospheric effects upon air quality and climate due to policy changes regarding complex emissions (such as solvent and petrochemical evaporation) to be better assessed.

国际社会对空气质量恶化和气候变化的反应是由数值模型的预测指导的。这些模型包含对自然和人类活动中微量气体和气溶胶未来排放、它们在整个大气中的扩散以及它们化学转化为各种次级产品的估计。对流层中的光氧化非常复杂，由短命自由基物种引发，白天主要由羟基自由基 OH 主导，而夜间则由 NO3 自由基或臭氧主导。化学氧化循环消除了对人类（例如CO）或更广泛的环境（温室气体，例如CH4）直接有害的主要排放痕量物质。然而，大气光氧化产生的许多二次产物也是直接有害的，例如O3、NO2、酸性和多功能物质，其中许多挥发性低，能够有效地分配到凝聚相，产生二次有机污染物。气溶胶 (SOA)。为了计算 OH 的丰度，从而计算大气中其他微量气体的寿命，有必要了解生成和去除 OH 过程的反应速率的基本知识。 OH 与有机和无机物质发生反应，前者在任何 OH 计算中都会产生很大的不确定性，因为空气中存在数千种反应性挥发性有机化合物 (VOC)。实际上，不可能识别空气中存在的所有挥发性有机化合物，即使以全面的方式尝试识别，反应速率的动力学数据也经常丢失。 VOC 的复杂性和有限的相关数据使得观测到的 OH 浓度和 OH 反应性与模型计算之间的协调性本质上很困难。当尝试时，观察到显着的不匹配，凸显了我们模拟对流层化学的能力中的一些基本缺陷。最近对 OH 反应性的测量与 VOC 的测量相结合，使得缺失的 OH 汇的大小得以量化，但无法量化其化学特性。其他测量表明，当使用全面的二维气相色谱作为测量技术时，环境空气中存在许多未识别的有机成分。该提案首次将约克的 Lewis 和 Hamilton 开发的超高分辨率 VOC 测量与 FAGE free-由利兹的 Heard、Whalley 和 Rickard 开发的激进测量和 MCM 建模技术。我们将确定有助于去除 OH 的缺失有机材料的身份，并评估其氧化过程中降解产物的形成。这将通过将综合二维气相色谱仪与飞行时间质谱仪和氢火焰离子化检测器与 OH 化学反应器相结合来实现。通过将环境空气样品暴露于含有增强 OH 自由基的受控环境中，并观察未知物质的色谱峰强度相对于已知 VOC 物质（且与 OH 的反应性已知）强度变化的相对变化，可得到 OH将确定未知物种的反应性。使用质谱检测器将使我们能够积极地识别那些我们观察到对 OH 汇有显着贡献的物种，并提供对所形成的次级产物的形成速率的评估。使用造成损失的主要物种的功能组分类，我们将创建用于 MCM 的替代参数化机制，以便更准确地描述控制城市 OH 和 O3 的过程。了解缺失反应性的功能将使大气对由于复杂排放（例如溶剂和石化蒸发）的政策变化而导致的空气质量和气候需要得到更好的评估。

项目成果

The MCM v3.3.1 degradation scheme for isoprene

• DOI: 10.5194/acp-15-11433-2015
• 发表时间: 2015-01-01
• 期刊: ATMOSPHERIC CHEMISTRY AND PHYSICS
• 影响因子: 6.3
• 作者: Jenkin, M. E.;Young, J. C.;Rickard, A. R.
• 通讯作者: Rickard, A. R.

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

激光闪光光解与激光诱导荧光光谱法测量 OH 反应性

• DOI: 10.5194/amt-2016-51
• 发表时间: 2016
• 作者: Stone D

Supplementary material to "A self-consistent, multi-variate method for the determination of gas phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical"

补充材料

• DOI: 10.5194/acp-2017-917-supplement
• 发表时间: 2017
• 作者: Shaw J

A self-consistent, multi-variate method for the rapid determination of gas phase rate coefficients, applied to reactions of atmospheric VOC with multiple radical oxidants

一种快速测定气相速率系数的自洽多变量方法，适用于大气 VOC 与多种自由基氧化剂的反应

• 发表时间: 2017
• 作者: Shaw, J.

A self-consistent, multivariate method for the determination of gas-phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical

• DOI: 10.5194/acp-18-4039-2018
• 发表时间: 2017-10
• 期刊: Atmospheric Chemistry and Physics
• 影响因子: 6.3
• 作者: J. Shaw;R. Lidster;D. Cryer;N. Ramírez;Fiona C. Whiting;Graham A Boustead;L. Whalley;T. Ingham;A. Rickard;R. Dunmore;D. Heard;A. Lewis;L. Carpenter;J. Hamilton;T. Dillon