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组成、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了证据，表明在清洁、偏远的环境中通常了解OH和氢过氧基(HO2)化学，但在氮氧化物(NOx)水平较高的城市则不太了解。其他证据表明，在低NOx、高生物来源VOC(BVOC)的环境中，对OH的了解最少，特别是在森林中，测量到的OH大大超过了模拟OH的2到10倍，远远超出了典型的±30%2ó的不确定度。这些森林环境正在挑战正在设计新的氧化机制的模型和测量，这些测量可能会有干扰，并接近其检测下限。最近，首席调查者(PI)基于激光的地面氢氧化物传感器(GTHOS)通过在通常的方法(称为OHchem)上增加了通过化学去除OH来检测OH的能力，从而确认了对O3、OH和烯烃组合的先前怀疑的干扰。实验室测试证明OHchem是GTHOS的真正的OH。该项目将为一项多调查者研究贡献OHchem、OHwave、HO2、基于烯烃的RO2和OH的反应性测量，该研究将提供异戊二烯氧化机理的一致图片，证明OHchem是真正的OH，并确定GTHOS OH干扰是否是由与大气相关的中间物种引起的。PI还将找到GTHOS对这种臭氧/羟基/烯烃干扰比其他羟基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这种灵敏度。这项为期两年的研究的这些目标将主要通过与其他小组一起参与单独提出的异戊二烯化学实验(FIX)来实现，该实验包括作为二次有机气溶胶研究一部分的现场部分和实验室环境舱部分。这项研究的结果将改进区域和全球空气质量模型中的氧化机制，从而为政策制定者提供更好的指导。

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.