Urban oxidising capacity measurements using inert and reactive tracers

使用惰性和反应性示踪剂测量城市氧化能力

• 批准号: NE/K014811/1
• 负责人: Carl Percival
• 金额: $ 33.32万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FK014811%2F1
• 关键词: Urban; oxidising; capacity; measurements; using

By definition, the urban environment is one where many people either live or work. During the course of a day, people will be outdoors for varying lengths of time and be exposed to different levels of air pollutants. During daytime, sunlight can provide the energy needed to produce the hydroxyl radical (written as HO), which is an extremely reactive species that acts like a detergent in the atmosphere, reacting with air pollutants. Therefore, we want to know how much HO there is in the urban atmosphere and how its level changes over the course of a day and from day to day as a function of time of the year. It is possible to measure HO directly using an instrument called FAGE and this has been carried out for some cities in the UK (e.g. Birmingham and London). These data have helped us to understand how HO varies in one location but the instrument FAGE is too expensive to replicate to allow us to make measurements across a city. HO is made and destroyed very rapidly, so a measurement of HO also tells us the ratio of the rate of its production to the rate of its removal and indeed FAGE can also tell us about the rate of its removal. Therefore, we can calculate the rate of production from these measurements, but these other measurements from a number of cities suggest that the rate of production of HO is underestimated based on our current understanding. One possibility is that there are missing sources that we don't know about? Given the importance of HO and other oxidants to urban air quality it is vital to try to work out what these missing sources are.With this in mind we have developed a new technique to allow us to measure the amount of HO (and other detergents) pollutants encounter as they move through the urban environment. In this way we will be able to build up a picture of how removal rates for pollutants varies across a City as a function of time of day, season, pollution loading etc. We will also be able to estimate how rapidly particles are made in the urban environment and begin to understand what controls their production. Particles can be released into the atmosphere directly, e.g. from car exhausts, (called primary particles) but can also be made in the atmosphere, a so called secondary particles. We want to know more about the sources of secondary particles as we can make reasonable estimates of primary particle sources. Particles are known to be bad for air quality and a reduction in levels would be of great benefit. In order to make these measurements we will release small amounts of organic molecules that react with oxidants such as HO and some molecules that don't react with anything. We have tagged the reactive molecules so we can tell them apart from ones that are there already into the city and will measure the levels of both reactive and inert species downwind of the release point. As these molecules disperse their level will drop because of dilution and the inert species will tell us the dilution rate, the reactive ones will drop even more as they will not only disperse but also react. By using these two pieces of information we can estimate their chemical removal rates and hence the amount of HO present. Other measurements of pollutants and meteorology will be made at the same time and we will then be able to estimate how quickly these pollutants are removed. Computer models that contain our current knowledge of urban air quality will be compared with all the measurement data and we will then be able to test a number of hypotheses for the missing source of HO and other oxidants. We will also carry out studies at night where HO levels are very low and a different oxidant called the nitrate radical (NO3) takes over. We have an instrument that can make measurements of NO3 and so we can compare the measurement of NO3 in one location with the NO3 experienced by pollutants as they pass through the city. In this way a detailed comparison can be made

根据定义，城市环境是许多人生活或工作的环境。在一天的过程中，人们将在不同的时间范围内在户外，并暴露于不同水平的空气污染物。在白天，阳光可以提供产生羟基自由基（写为HO）所需的能量，这是一种极具反应性的物种，其作用像在大气中的洗涤剂，与空气污染物反应。因此，我们想知道城市气氛中有多少ho，以及它的水平在一天中的一年中，每天的变化如何随着一年的时间而变化。可以使用名为Fage的乐器直接测量HO，这是为英国（例如伯明翰和伦敦）的一些城市进行的。这些数据帮助我们了解了HO在一个位置的变化，但是仪器的装备太昂贵了，无法复制，无法让我们在整个城市进行测量。 HO的制造和破坏非常迅速，因此HO的测量还告诉我们其生产率与其去除率的比率，实际上，Fage也可以告诉我们其去除速度。因此，我们可以从这些测量值中计算出生产率，但是许多城市的其他测量结果表明，基于我们当前的理解，HO的生产率被低估了。一种可能是我们不知道的缺少资源吗？鉴于HO和其他氧化剂对城市空气质量的重要性，尝试确定这些缺失的资源是至关重要的。考虑到这一点，我们已经开发了一种新技术，使我们能够测量在城市环境中移动时HO（和其他洗涤剂）污染物的数量。通过这种方式，我们将能够建立污染物的去除率在整个城市中如何随着一天中的时间，季节，污染加载等方面的变化而变化。我们还将能够估计在Urban环境中颗粒的速度迅速，并开始理解控制其产量的原因。颗粒可以直接释放到大气中，例如从汽车排气中（称为主颗粒），但也可以在大气中制成，即所谓的二级颗粒。我们想更多地了解次级粒子的来源，因为我们可以对主要粒子来源进行合理的估计。众所周知，颗粒对空气质量不利，降低水平将是很大的好处。为了进行这些测量，我们将释放少量与氧化剂（如HO）和某些与任何任何反应的分子反应的有机分子。我们已经标记了反应性分子，因此除了已经进入城市的分子外，还可以测量释放点下风的反应性和惰性物种的水平。由于这些分子分散的水平会由于稀释而下降，并且惰性物种会告诉我们稀释率，反应性稀释率会下降更多，因为它们不仅会分散，而且会反应。通过使用这两个信息，我们可以估计它们的化学去除率，从而估计HO的量。将同时进行污染物和气象学的其他测量，然后我们将能够估计去除这些污染物的速度。将我们当前关于城市空气质量知识的计算机模型与所有测量数据进行比较，然后我们将能够测试HO和其他氧化剂缺失来源的许多假设。我们还将在夜间进行研究，其中HO水平非常低，并且一种称为硝酸盐自由基（NO3）接管的氧化剂。我们有一种可以进行NO3测量的工具，因此我们可以将一个位置的NO3与污染物经过城市经历的NO3进行比较。这样可以进行详细的比较