HOx and NOx production in oxidation flow reactors via photolysis of isopropyl nitrite, isopropyl nitrite-d7, and 1,3-propyl dinitrite at λ = 254, 350, and 369 nm Atmospheric Measurement Techniques

Oxidation flow reactors (OFRs) are an emerging technique for studying the formation and oxidative aging of organic aerosols and other applications. In these flow reactors, hydroxyl radicals (OH), hydroperoxyl radicals (HO2), and nitric oxide (NO) are typically produced in the following ways: photolysis of ozone (O3) at λ=254 nm, photolysis of H2O at λ=185 nm, and via reactions of O(1D) with H2O and nitrous oxide (N2O); O(1D) is formed via photolysis of O3 at λ=254 nm and/or N2O at λ=185 nm. Here, we adapt a complementary method that uses alkyl nitrite photolysis as a source of OH via its production of HO2 and NO followed by the reaction NO + HO2 → NO2 + OH. We present experimental and model characterization of the OH exposure and NOx levels generated via photolysis of C3 alkyl nitrites (isopropyl nitrite, perdeuterated isopropyl nitrite, 1,3-propyl dinitrite) in the Potential Aerosol Mass (PAM) OFR as a function of photolysis wavelength (λ=254 to 369 nm) and organic nitrite concentration (0.5 to 20 ppm). We also apply this technique in conjunction with chemical ionization mass spectrometer measurements of multifunctional oxidation products generated following the exposure of α-Pinene to HOx and NOx obtained using both isopropyl nitrite and O3 + H2O + N2O as the radical precursors.

氧化流动反应器（Oxidation Flow Reactors, OFRs）是一类新兴实验技术，可用于研究有机气溶胶的生成与氧化老化过程，亦可拓展至其他相关应用领域。在该类反应器中，羟基自由基（hydroxyl radicals, OH）、过氧羟基自由基（hydroperoxyl radicals, HO₂）与一氧化氮（nitric oxide, NO）通常通过以下方式生成：在波长λ=254 nm条件下对臭氧（O₃）进行光解、在λ=185 nm条件下对水（H₂O）进行光解，以及通过1D态氧原子（O(¹D)）分别与H₂O、一氧化二氮（nitrous oxide, N₂O）发生反应；而1D态氧原子（O(¹D)）可通过在λ=254 nm条件下光解O₃，或在λ=185 nm条件下光解N₂O制得。
本研究采用了一种补充性实验方法：通过亚硝酸烷基酯光解生成HO₂与NO，再经由反应NO + HO₂ → NO₂ + OH来制备OH自由基，以此作为OH的来源。
本研究针对潜在气溶胶质量氧化流动反应器（Potential Aerosol Mass, PAM OFR）中，通过C3亚硝酸烷基酯（包括亚硝酸异丙酯、全氘代亚硝酸异丙酯与1,3-丙二亚硝酸酯）光解所产生的OH暴露量与氮氧化物（NOₓ）水平，开展了实验与模型表征分析，分析变量涵盖光解波长（λ=254 nm至369 nm）与有机亚硝酸酯浓度（0.5 ppm至20 ppm）。
本研究还将该技术与化学电离质谱仪（chemical ionization mass spectrometer）检测手段相结合，针对以亚硝酸异丙酯、O₃ + H₂O + N₂O作为自由基前体制得的HOₓ与NOₓ体系，对α-蒎烯（α-Pinene）经其氧化后生成的多官能团氧化产物进行了检测分析。