Measurement of the OH chemical lifetime, concentrations of speciated RO2 radicals, and a new method for the field detection of OH radicals

大气中短寿命活性中间体的浓度，例如OH、HO 2和过氧自由基（RO 2），是由当地原位化学而不是由传输过程决定的。羟基自由基（OH）是大气中的天然清洁剂，可清除大部分痕量气体，而过氧自由基与一氧化氮反应产生地面臭氧。因此，这些自由基是验证大气模型中化学机制准确性的理想目标物质。化学性质的准确性非常重要，因为这些机制是化学运输/全球环流/区域空气质量模型的核心，这些模型用于预测我们大气的未来组成，从而预测未来生物和人为排放变化导致的气候或空气质量的任何相关变化。在现场进行的激进测量与模型计算的比较提供了一个常用的框架，以检查模型是否能够充分描述一系列清洁和污染环境的基础化学。在本提案中，我们将开发新的仪器，以提供现场测量与模型计算进行比较。我们将测量OH的化学寿命，它告诉我们OH通过与所有汇的反应从大气中去除的速率。通过与模型计算的OH寿命的比较，我们可以知道OH的汇是否在模型中得到了充分的体现。如果存在分歧，这可以解释为什么模型不能准确地再现测量的OH浓度。过氧自由基与大气中的氮氧化物反应，导致臭氧形成，但目前的现场仪器通常只能测量其总浓度。我们将开发一种新的检测方法，这是密切相关的FAGE技术，我们已经成功地用于测量OH和HO 2自由基，以实现一些形态的过氧自由基的测量。该提案还旨在开发一种在现场检测OH的新方法，该方法基于OH与钠二聚体的反应，产生发光的激发钠原子。该方法成本相对较低，重量轻，并提供了从广泛的位置与长期能力的OH测量的潜力。本提案中开发的设备将安装在一个新的装有仪器的车辆中，并在实地活动中部署。

The concentrations of short-lived reactive intermediates in the atmosphere, for example OH, HO2 and peroxy radicals (RO2), are determined by local in situ chemistry and not by transport processes. The hydroxyl radical (OH) is the natural cleanser in the atmosphere, and removes the majority of trace gases, whereas peroxy radicals react with nitric oxide to generate ground-level ozone. Therefore, these radicals are ideal target species with which to validate the accuracy of chemical mechanisms within atmospheric models. It is very important that the chemistry is accurate, as these mechanisms are at the heart of chemistry-transport/global circulation/regional air quality models that are used to predict the future composition of our atmosphere, and hence any associated changes in climate or air quality as a result of future changes in biogenic and anthropogenic emissions. Comparison of radical measurements made in the field with model calculations provides a commonly-used framework to examine whether the models are able to adequately describe the underlying chemistry for a range of clean and polluted environments. In this proposal we will develop new instruments to provide field measurements for comparison with model calculations. We will make measurements of the chemical lifetime of OH, which tells us the rate at which OH is removed from the atmosphere through reaction with all of its sinks. Comparison with the OH lifetime calculated by models tells us whether the sinks of OH are adequately represented in the model. If there is disagreement this could explain why models are not able to accurately reproduce measured OH concentrations. Peroxy radicals react with nitrogen oxide in the atmosphere leading to ozone formation, yet current field instruments are normally only able to make a measurement of their total concentration. We will develop a new detection method that is closely related to the FAGE technique that we have successfully used to measure OH and HO2 radicals, in order to achieve some speciation for the measurement of peroxy radicals. The proposal also aims to develop a new method for the detection of OH in the field, based on a reaction of OH with the sodium dimer producing an excited sodium atom that emits light. The method is relatively low-cost and lightweight, and offers potential for OH measurements from a wide range of locations with long-term capability. The apparatus developed in this proposal will be housed in a new, instrumented vehicle and deployed during field campaigns.