Determination of uptake coefficients for heterogeneous loss of HO2 radicals to atmospheric aerosols

大气气溶胶中 HO2 自由基异质损失吸收系数的测定

基本信息

批准号：
NE/F020651/1
负责人：
Dwayne Heard
金额：
$ 42.39万
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：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF020651%2F1
关键词：
Determination uptake coefficients heterogeneous loss

项目摘要

The free-radicals OH, HO2 and RO2 mediate virtually all of the oxidative chemistry in the lower atmosphere, being responsible for the transformation of primary emissions into secondary pollutants such as NO2, O3 and particulates. Free-radicals control the lifetime of climate gases (e.g. CH4), the budget of O3, and the production of acidic species. Understanding the behaviour of free-radicals in the atmosphere is of paramount importance in understanding the lifetime and spatial scales of pollutant transport. Predictive models for future air quality and climate change contain complex chemical schemes, and comparison with measurements of free-radicals in the present atmosphere constitutes the best validation of these schemes. Some field campaigns report significant discrepancies between models and in situ observations of OH and HO2 radicals (HOx), for example in marine and urban environments. Heterogeneous losses of HO2 to aerosol have been invoked to explain these differences. Reactions of HO2 on cloud droplets and cirrus particles have also been invoked to explain model discrepancies for HOx in the upper troposphere. However, the heterogeneous and multiphase chemistry of HOx is relatively understudied, and there is considerable variation in the literature for HO2 uptake coefficients, determined in the laboratory under limited conditions of temperature/relative humidity and aerosol type. In addition, these experiments were performed at relatively high concentrations of HO2 where second order loss via the HO2 self-reaction was dominant over the first order heterogeneous loss, complicating the extraction of accurate values. The primary aim of this project is to use the FAGE (Fluorescence Assay by Gas Expansion) technique to measure HO2 with exquisite sensitivity (0.04 pptv detection limit) so that its concentration can be kept extremely low such that the rate of the gas phase self-reaction is negligible compared with the rate of heterogeneous loss, which will be measured in an aerosol flow-tube. Measurements of HO2 uptake coefficients using aerosols with a range of diameters and composition relevant to the atmosphere (H2SO4, (NH4)2SO4, sea salt, oleic acid and soot) will be made, and data recorded under different temperatures, relative humidities and pH will enable parameterisations to be obtained. The results will be exploited through incorporation into a box model to re-evaluate the role of heterogeneous loss for two previous campaigns held in marine and urban environments.

自由基OH，HO2和RO2在低大气中介导了几乎所有的氧化化学，负责将一级排放转化为二级污染物，例如NO2，O3和颗粒。自由基控制气候气体的寿命（例如CH4），O3的预算和酸性物种的生产。了解自由基在大气中的行为对于理解污染物运输的生命周期和空间尺度至关重要。未来空气质量和气候变化的预测模型包含复杂的化学方案，并与当前大气中自由基的测量值进行比较构成了这些方案的最佳验证。一些现场活动报告了模型与原位观察到OH和HO2激进分子（HOX）之间的严重差异，例如在海洋和城市环境中。已经调用了HO2向气溶胶的异质损失来解释这些差异。还调用了HO2对云滴和卷卷颗粒的反应，以解释对流层上部HOX的模型差异。然而，在有限的温度/相对湿度和气溶胶类型的有限条件下，在实验室确定的HO2吸收系数的文献中，HOX的异质性和多相化学相对研究。另外，这些实验是在相对较高的HO2浓度下进行的，其中通过HO2自反应的二阶损失在一阶的异质损失上占主导地位，从而使提取准确值的提取变得复杂。该项目的主要目的是使用装饰（通过气体膨胀）技术以精致的灵敏度（0.04 PPTV检测极限）测量HO2，以使其浓度保持极低，以使气相自相相的速率自动相位。与异质损失率相比，反应可以忽略不计，这将在气溶胶流管中进行测量。使用与大气相关的一系列直径和组成的气溶胶（H2SO4，（NH4）2SO4，海盐，油酸和烟灰）对HO2摄取系数的测量，并在不同的温度下记录数据，相对湿度和pH将记录下来启用参数化。结果将通过纳入框模型来利用，以重新评估在海洋和城市环境中进行的两个运动中的异质损失的作用。