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Total Ozone Reactivity: A new measurement of volatile organic compounds in the atmosphere

臭氧总反应性：大气中挥发性有机化合物的新测量方法

基本信息

批准号：
NE/P003524/1
负责人：
William Bloss
金额：
$ 15.96万
依托单位：
University of Birmingham
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP003524%2F1
关键词：
Total Ozone Reactivity new measurement

项目摘要

Gaseous hydrocarbons - volatile organic compounds (VOCs) - are key atmospheric components. They may be air pollutants, harmful to human health in their own right, and some are greenhouse gases. Atmospheric chemical processing of VOCs leads to the formation of secondary pollutants such as ozone and secondary organic aerosol - which adversely affect health, damage vegetation (reducing crop yields by 5 - 15% globally) and affect climate. A quantitative understanding the atmospheric VOC budget underpins many aspects of atmospheric science.However, quantifying the VOC budget is a challenging goal, as very many atmospheric VOCs are emitted, each of which produces a cascade of degradation products - numbering over order-of-10^5 individual chemical species from larger VOCs. This is particularly the case for biogenic VOCs (BVOCs) which tend to be larger, more chemically complex molecules, and which dominate non-methane VOC emissions globally. Traditional approaches, in which individual species are measured, quickly run up against this barrier of chemical complexity and cannot assess the total VOC budget - consequently, we are unable to fully quantify the total potential for secondary pollutant formation from VOC oxidation.An alternative approach is to measure an integrated property of all VOCs present - such as their chemical reactivity, the rate at which a given atmospheric oxidant reacts with all VOCs present. This determines the reactive potential of all VOCs - both those identified and those unmeasured - providing a metric directly related to secondary pollutant formation. This approach has been successfully trialled for OH radicals, and measures of the OH reactivity have shown that attempting to measure each individual species by conventional approaches may underestimate the VOC budget by up to 90%. While OH radicals dominate oxidation of many VOCs during the day, for alkene species (such as the majority of biogenic VOCs) reaction with ozone is also important - dominant at night, and as important as OH during the day for the larger BVOCs, mono- and sesquiterpenes, which are the most challenging to measure with conventional approaches. Therefore, measurement of the total ozone reactivity has potential to provide new insight into the total budget of reactive BVOCs present in the atmosphere, and the extent to which it is currently substantially underestimated - a hypothesis attracting growing support from a range of recent measurements.Within this project, we will develop a prototype ozone reactivity instrument, building upon a feasibility study carried out in our laboratory; we will test the system performance with individual VOC standards, and with complex VOC mixtures from plant specimens in laboratory enclosures, and we will demonstrate its applicability to assess the change in BVOC emissions from whole trees in response to environmental stress. This latter objective will be achieved through measurements at the internationally unique whole tree chambers at the Hawkesbury Forest Experiment (HFE) site in Richmond, NSW, where we will measure changes in total ozone reactivity from eucalyptus trees as a function of changing RH, temperature and CO2 abundance (400 ppm [i.e. present day] vs 640 ppm). Within the duration of this project, only limited experiments may be undertaken - but these will provide a unique insight into the response of total BVOC emissions from vegetation to environmental change, underpinning future exploitation of the approach.Completion of the project will achieve technology readiness level (TRL) 4 - basic validation in a controlled environment. Following this proof-of-concept work (i.e. outside this proposal), we have identified an opportunity for initial field deployment of the technique, to perform the first measurements of total BVOC ozone reactivity in ambient air, from a mature Oak woodland under conditions of present day and anticipated future CO2 levels.

气态碳氢化合物--挥发性有机化合物(VOCs)--是大气中的关键成分。它们可能是空气污染物，本身就对人类健康有害，有些是温室气体。对VOCs的大气化学处理会导致臭氧和二次有机气溶胶等二次污染物的形成，这些污染物会对健康造成不利影响，破坏植被(使全球农作物产量减少5-15%)，并影响气候。对大气VOC预算的定量理解是大气科学的许多方面的基础。然而，VOC预算的量化是一个具有挑战性的目标，因为大气中排放了非常多的VOCs，每一种都会产生一系列降解产物--来自较大VOCs的单个化学物种的数量超过10^5个数量级。尤其是生物来源的VOCs(BVOCs)，它们往往是更大、更复杂的化学分子，并且在全球非甲烷VOC排放中占据主导地位。传统的测量单个物种的方法很快就会遇到化学复杂性的障碍，无法评估总的VOC预算--因此，我们无法完全量化VOC氧化形成二次污染物的总潜力。另一种方法是测量所有存在的VOC的综合性质--例如它们的化学反应活性，即给定的大气氧化剂与所有存在的VOCs反应的速度。这决定了所有VOCs的反应潜力--包括那些已识别的和那些未测量的--提供了与二次污染物形成直接相关的指标。这种方法已经成功地用于OH自由基的试验，并且OH反应性的测量表明，试图用传统方法测量每个单独的物种可能会低估VOC预算高达90%。虽然OH自由基在白天主导了许多VOCs的氧化，但对于烯烃物种(如大多数生物来源的VOCs)来说，与臭氧的反应也是重要的--在夜间占主导地位，对于较大的BVOCs、单萜和倍半萜来说，在白天与OH的反应同样重要，这些都是用传统方法测量最具挑战性的。因此，臭氧总反应性的测量有可能提供对大气中活性BVOCs的总预算以及目前被大大低估的程度的新见解--这一假设得到了最近一系列测量的越来越多的支持。在这个项目中，我们将在我们实验室进行的可行性研究的基础上，开发一个臭氧反应性原型仪器；我们将使用单独的VOC标准和实验室围栏中植物样本的复杂VOC混合物来测试系统性能，并将证明其适用于评估整个树木的BVOC排放随环境压力的变化。后一个目标将通过在新南威尔士州里士满的霍克斯伯里森林实验(HFE)地点的国际独一无二的整树室进行测量，在那里我们将测量桉树的总臭氧反应性随着相对湿度、温度和二氧化碳丰度(400ppm[即现在的]对640ppm)的变化而发生的变化。在该项目的持续时间内，可能只会进行有限的实验--但这些实验将提供一个独特的视角，了解植物总BVOC排放对环境变化的反应，为未来开发该方法奠定基础。该项目的完成将达到技术准备级别(TRL)4-在受控环境中进行基本验证。在这项概念验证工作之后(即在这项提议之外)，我们已经确定了初步现场部署技术的机会，以在当前和预期的未来二氧化碳水平的条件下，从成熟的橡树林地对环境空气中的BVOC臭氧总反应性进行首次测量。