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。测量值和模型的比较提供了证据，表明OH和氢过氧（HO2）的化学性质通常在清洁、偏远的环境中被了解，但在氮氧化物（NOx）水平较高的城市中却知之甚少。其他证据表明，在低氮氧化物、高生物源VOC （BVOC）环境中，对OH的了解最为有限，特别是在森林中，测量到的OH已大大超过模拟的OH的2至10倍，远远超出了典型的±30% 2ó不确定性。这些森林环境对模型和测量提出了挑战，这些模型正在设计新的氧化机制，而测量可能有干扰，接近检测极限。最近，在首席研究员（PI）的基于激光的地基氢氧化物传感器（GTHOS）中，通过在OH光谱线（称为OHwave）的常用波长调制方法上增加OH的化学去除（称为OHchem）来检测OH的能力，证实了先前怀疑的O3， OH和烯烃的干扰。实验室测试表明OHchem是GTHOS的真正OH。该项目将对OHchem、OHwave、HO2、烯烃基RO2和OH的反应性进行测量，为一项多研究者的研究提供异戊二烯氧化机制的一致图像，证明OHchem是真正的OH，并确定GTHOS OH干扰是否由大气相关的中间物质引起。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时降低灵敏度。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，这些小组分别在一个聚焦异戊二烯化学实验（FIX）中提出建议，该实验有一个作为二次有机气溶胶研究的一部分的现场组成部分和一个实验室环境室组成部分。这项研究的结果将改进用于区域和全球空气质量的模型中的氧化机制，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.