Oxidation flow reactors (OFRs) efficiently produce OH radicals using low-pressure Hg-lamp emissions at λ = 254 nm (OFR254) or both λ = 185 and 254 nm (OFR185). OFRs under most conditions are limited to studying low-NO chemistry (where RO₂ + HO₂ dominates RO₂ fate), even though substantial amounts of initial NO may be injected. This is due to very fast NO oxidation by high concentrations of OH, HO₂, and O₃. In this study, we model new techniques for maintaining high-NO conditions in OFRs, that is, continuous NO addition along the length of the reactor in OFR185 (OFR185-cNO), recently proposed injection of N₂O at the entrance of the reactor in OFR254 (OFR254-iN₂O), and an extension of that idea to OFR185 (OFR185-iN₂O). For these techniques, we evaluate (1) fraction of conditions dominated by RO₂ + NO while avoiding significant nontropospheric photolysis and (2) fraction of conditions where reactions of precursors with OH dominate over unwanted reactions with NO₃. OFR185-iN₂O is the most practical for general high-NO experiments because it represents the best compromise between experimental complexity and performance upon proper usage. Short lamp distances are recommended for OFR185-iN₂O to ensure a relatively uniform radiation field. OFR185-iN₂O with low O₂ or using Hg lamps with higher 185 nm-to-254 nm ratio can improve performance. OFR185-iN₂O experiments should generally be conducted at higher relative humidity, higher UV, lower concentration of non-NO_y external OH reactants, and percent-level N₂O. OFR185-cNO and OFR185-iN₂O at optimal NO precursor injection rate (∼2 ppb/s) or concentration (∼3%) would have satisfactory performance in typical field studies where ambient air is oxidized. Exposure estimation equations are provided to aid experimental planning. This work enables improved high-NO OFR experimental design and interpretation.

中文翻译：

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用于研究OH引发的大气化学反应的氧化流反应器中维持高NO条件的新技术的模型评估

氧化流反应器（OFR）使用低压Hg灯在λ= 254 nm（OFR254）或同时在λ= 185和254 nm（OFR185）处发射汞，可有效地产生OH自由基。即使可以注入大量的初始NO ，大多数情况下的OFR仅限于研究低NO化学（其中RO ₂ + HO ₂主导RO _2的命运）。这是由于高浓度的OH，HO ₂和O ₃导致NO氧化非常快。在这项研究中，我们对维持OFR中高NO条件的新技术进行建模，即沿OFR185的反应堆长度连续添加NO（OFR185-cNO），最近建议在反应堆入口处注入N ₂ O在OFR254（OFR254-iN ₂O），并将其扩展到OFR185（OFR185-iN ₂ O）。对于这些技术，我们评估（1）以RO ₂ + NO为主的条件部分，同时避免显着的非对流层光解作用；以及（2）以前体与OH的反应为主而不是与NO _3的反应为主的条件。OFR185-iN ₂ O在一般的高NO实验中是最实用的，因为它代表了正确使用后实验复杂性和性能之间的最佳折衷。对于OFR185-iN ₂ O，建议使用较短的灯距离，以确保相对均匀的辐射场。OR185-iN ₂ O低O ₂或使用比185 nm至254 nm高的汞灯可以提高性能。OFR185-iN ₂ O实验通常应在较高的相对湿度，较高的紫外线，较低的非NO _y外部OH反应物浓度和百分含量的N ₂ O下进行。OFR185-cNO和OFR185-iN ₂ O在最佳NO前体下进行在典型的现场空气被氧化的现场研究中，注入速率（〜2 ppb / s）或浓度（〜3％）将具有令人满意的性能。提供了暴露估计方程式，以帮助进行实验计划。这项工作可以改善高NO OFR实验设计和解释。