Resolving Issues of Hydrogen Oxides Measurements: Laboratory Studies of HOx-NOx Chemistry and Measurement Intercomparisons

本项目致力于改进大气中羟基和过氧化氢自由基(OH和HO2)的测量方法。这些化合物具有很强的活性，而且已知可以净化？通过氧化和分解一些痕量物种和污染物，使它们从大气中消失。了解大气氧化化学对于建立大气组成、空气质量和气候变化之间的联系至关重要。测量OH和HO2的一种方法是使用地基对流层氢氧化物传感器(GTHOS)的气体膨胀荧光分析(FAGE)仪器。过去，GTHOS/FAGE的实测值与OH和HO2的模型值之间存在差异，主要表现在低氮氧化物(NOx)环境中的OH高于预期，而在高NOx环境中的HO2高于预期。建议的工作包括三个主要任务：(1)确定测量仪器(GTHOS/FAGE)中OH干扰的原因，并实施仪器更换，以将其对OH测量的影响降至最低；(2)通过有重点的实验室研究解决HOx-NOx化学问题；以及(3)将GTHOS的检测下限降低到105OH cm-3，绝对不确定度降低到20%(95%置信度)。这一建议很有可能改变目前对大气化学的理解，包括空气污染化学和对这种化学变化做出反应的辐射活性物种对全球气候的强迫。

This project is focused on improving measurement methods for hydroxyl and hydroperoxyl radicals (OH and HO2) in the atmosphere. These compounds are very reactive and known to ?cleanse? the atmosphere by oxidizing and breaking down a number of trace species and pollutants so that they are removed from the atmosphere. Understanding atmospheric oxidation chemistry is critical for establishing the links between atmospheric composition, air quality, and climate change.One method for measuring OH and HO2 is the Fluorescence Assay by Gas Expansion (FAGE) instrument using a Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS). In the past, there have been discrepancies between the GTHOS/FAGE measured values and the modeled values of OH and HO2, primarily showing greater-than-expected OH in low-nitrogen oxides (NOx) environments and greater-than-expected HO2 in high-NOx environments.The proposed effort consists of three main tasks: (1) identifying the cause of the OH interference in the measurement instrument (GTHOS/FAGE) and implementing instrument changes to minimize its impact on OH measurement; (2) resolving the issues of HOx-NOx chemistry with focused laboratory studies; and (3) lowering the GTHOS limit-of-detection to 105 OH cm-3 and the absolute uncertainty to 20% (95% confidence).This proposal has a high potential to transform current understanding of atmospheric chemistry, including air pollution chemistry and the forcing of global climate by radiatively active species that respond to changes in this chemistry.