Resolving Issues of Hydroxyl (OH) Measurements and Oxidation Chemistry in Forest Environments

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。羟基（OH）是大气的主要氧化剂。测量和模型的比较提供的证据表明，OH和过氧化氢（HO 2）的化学通常是在清洁，偏远的环境中理解，但在城市时，氮氧化物（NOx）的水平很高，不太了解。其他证据表明，在低NOx、高生物源VOC（BVOC）的环境中，对OH的了解最少，特别是在森林中，测量的OH大大超过模型OH的2到10倍，远远超过典型的± 30%2 <$不确定度。这些森林环境对模型提出了挑战，为此正在设计新的氧化机制，以及测量，其可能具有干扰并且接近其检测极限。一个以前怀疑的干扰最近被证实为O3，OH和烯烃的组合在主要研究者（PI）的基于激光的地面氢氧化物传感器（GTHOS）通过添加的能力，通过化学去除OH（称为OHchem）检测OH的常用方法波长调制和关闭的OH光谱线（称为OHwave）。实验室测试表明，OHchem是GTHOS的真实的OH。该项目将有助于测量OHchem，OHwave，HO 2，烯烃基RO 2和OH反应性的多研究者研究，将提供一个一致的图片异戊二烯氧化机制，证明OHchem是真实的OH，并确定GTHOS OH干扰是否是由大气相关的中间物种引起的。PI还将找到GTHOS对O3/OH/烯烃干扰比其他OH测量仪器更敏感的原因，并在干扰与大气无关的情况下降低灵敏度。这项为期两年的研究的这些目标将主要通过与其他小组的参与来实现，这些小组分别提出了一项重点异戊二烯化学实验（FIX），该实验具有作为二次有机气溶胶研究一部分的现场组成部分和实验室环境室组成部分。这项研究的结果将导致改进用于区域和全球空气质量模型的氧化机制，从而为决策者提供更好的指导。

Understanding atmospheric oxidation chemistry is critical for establishing the links between atmospheric composition, air quality, and climate change. Hydroxyl (OH) is the atmosphere's primary oxidant. Comparisons of measurements and models provide evidence that OH and hydroperoxyl (HO2) chemistry is generally understood in clean, remote environments, but less well understood in cities when nitrogen oxide (NOx) levels are high. Other evidence indicates that OH is most poorly understood in low-NOx, high biogenic VOC (BVOC) environments, particularly forests where measured OH has greatly exceeded modeled OH by a factor of 2 to 10, well beyond the typical ±30% 2ó uncertainties.These forest environments are challenging the models, for which new oxidation mechanisms are being designed, and the measurements, which can have interferences and be near their detection limits. A previously suspected interference was recently confirmed for the combination of O3, OH, and alkenes in the Principal Investigator's (PI) laser-based Ground-based Hydrogen Oxides Sensor (GTHOS) by adding the ability to detect OH by chemical removal of OH (called OHchem) to the usual method wavelength modulation on and off an OH spectral line (called OHwave). Laboratory tests demonstrate that OHchem is the real OH for GTHOS.This project will contribute measurements of OHchem, OHwave, HO2, alkene-based RO2, and OH reactivity to a multi-investigator study that will provide a consistent picture of the isoprene oxidation mechanism, demonstrate that OHchem is the real OH, and determine if the GTHOS OH interference is caused by an atmospherically relevant intermediate species. The PIs will also find the reason that GTHOS appears to be much more sensitive to this O3/OH/alkene interference than other OH-measuring instruments and to reduce that sensitivity if the interference is not atmospherically relevant. These goals of this two-year study will be accomplished primarily by participating with other groups who are proposing separately in a Focused Isoprene-chemistry eXperiment (FIX), which has a field component as part of the Secondary Organic Aerosol Study and a laboratory environmental chamber component. The results of this research will lead to improved oxidation mechanisms in the models that are used for regional and for global air quality, thus providing better guidance to policy makers.