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羟基自由基（OH和HO2）的测量方法。这些化合物具有很强的活性，可以“净化”。大气通过氧化和分解一些微量物质和污染物，使它们从大气中去除。了解大气氧化化学对于建立大气成分、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面对流层氢氧化物传感器（GTHOS）的气体膨胀荧光测定（FAGE）仪器。过去，GTHOS/FAGE的测量值与模拟的OH和HO2值存在差异，主要表现为低氮氧化物（NOx）环境下OH大于预期，高氮氧化物环境下HO2大于预期。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，并实施仪器更改以尽量减少其对OH测量的影响；(2)通过重点实验室研究解决HOx-NOx化学问题；(3)将GTHOS检测限降至105 OH cm-3，绝对不确定度降至20%（95%置信度）。这一建议极有可能改变目前对大气化学的理解，包括空气污染化学和响应这种化学变化的辐射活性物质对全球气候的强迫。

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.