NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
Phys Chem Chem Phys. 2018 Oct 3;20(38):24652-24664. doi: 10.1039/c8cp04193h.
The OH initiated oxidation of HNO3 in the UT/LS plays an important role in controlling the O3 budget, removing HOx radicals whilst driving NOx/y partitioning chemistry by yielding NO3 radicals: OH + HNO3 → H2O + NO3. In this paper, k1(T, P) was measured using OH (A ← X) Laser Induced Fluorescence (LIF) and the data was modelled over the 223-298 K temperature and 25-750 Torr pressure ranges, using the modified Lindemann-Hinshelwood expression , where k0 = 5.2 × 10-14 exp(200/T) cm3 s-1, k2 = 8.4 × 10-17 exp(1900/T) cm3 s-1 and k3 = 1.6 × 10-34 exp(1745/T) cm3 s-1. A significant source of experimental uncertainty derives from accurate determination of HNO3 concentration, which is impacted by heterogeneous uptake of the low volatility HNO3 onto cold surfaces of the reactors. Our results represent the determination of k1(T, P) using two different in situ [HNO3] measurements: VUV absorption and a new two photon Photolysis Induced Fluoresence (PIF). Experimental results are discussed along with a computational master equation calculation (MESMER), which highlight the need for further theoretical study into the OH + HNO3 mechanism and potential energy surface. The atmospheric impact of these new rate constants were modelled using the STOCHEM-CRI chemistry transport global model, which have shown a small reduction in global budgets of key atmospheric species, with more significant changes in the NOx/HNO3 ratio, peaking in the tropical upper troposphere regions.
OH 引发 UT/LS 中 HNO3 的氧化，在控制 O3 预算方面起着重要作用，通过生成 NO3 自由基去除 HOx 自由基，同时推动 NOx/y 分馏化学：OH + HNO3 → H2O + NO3。在本文中，使用 OH（A ← X）激光诱导荧光（LIF）测量了 k1（T，P），并使用修正的 Lindemann-Hinshelwood 表达式对 223-298 K 温度和 25-750 Torr 压力范围进行了建模，其中 k0 = 5.2 × 10-14 exp(200/T) cm3 s-1，k2 = 8.4 × 10-17 exp(1900/T) cm3 s-1 和 k3 = 1.6 × 10-34 exp(1745/T) cm3 s-1。实验不确定性的一个重要来源源于 HNO3 浓度的准确测定，这受到反应器冷表面上低挥发性 HNO3 的非均相吸收的影响。我们的结果代表了使用两种不同的原位[HNO3]测量方法（VUV 吸收和新的双光子光解诱导荧光（PIF））确定 k1（T，P）。实验结果与计算主方程（MESMER）一起进行了讨论，这突出表明需要对 OH + HNO3 机制和势能面进行进一步的理论研究。这些新速率常数对大气的影响使用 STOCHEM-CRI 化学输送全球模型进行了建模，该模型显示关键大气物种的全球预算略有减少，NOx/HNO3 比值变化更为显著，在热带对流层上部地区达到峰值。
