Data for: Nitration of polycyclic aromatic hydrocarbons adsorbed on silica gel and Fe2O3 particles with NO2: Effects of adsorbed water and hydrocarbons reactivity on kinetics and mechanism

The nitration of polycyclic aromatic hydrocarbons (PAHs) adsorbed on silica gel and Fe2O3 particles, which are known to be abundant in PM2.5, with NO2 (9.77 ppm) was studied using a fluidized-bed column to simulate the transformation of atmospheric PAHs at night. Anthracene, phenanthrene, pyrene, chrysene, fluoranthene, and perylene were used as PAHs, and the effects of water (H2Oads) adsorbed on the substrates and PAHs reactivity on kinetics and mechanism were investigated. On hydrated silica gel (H2Oads: 4.2 wt%), the most reactive perylene was nitrated by pseudo-first-order reaction, and moderately reactive PAHs (anthracene and pyrene) and less reactive chrysene were nitrated by H+-autocatalyzed reaction, while on dry Fe2O3 (H2Oads: 0.02 wt%), the nitration of the moderately reactive PAHs proceeded by pseudo-first-order reaction and less reactive chrysene proceeded by H+-autocatalyzed reaction. On the both substrates, the nitration of PAHs changed from pseudo-first-order to H+-autocatalyzed reactions as the reactivity of PAHs decreases, showing that the nitration kinetics and mechanism are affected by the concentration of H+ formed in H2Oads by NO2 exposure. On dry Fe2O3, most reactive perylene and the moderately reactive PAHs were nitrated by NO2, while on hydrated silica gel, the moderately reactive PAHs and chrysene were nitrated by NO2+, which would be formed via a pre-equilibrium between NO2 and H+ formed by NO2 exposure and released by the nitration. The formation of NO2+ is supported by the accelerated H+-autocatalyzed nitration on the H2SO4-adsorbed hydrated silica gel and by the report of NO2+ detection on hydrated borosilicate glass.本研究采用流化床柱模拟夜间大气中多环芳烃（polycyclic aromatic hydrocarbons, PAHs）的转化过程，针对PM2.5中丰度较高的硅胶与三氧化二铁（Fe₂O₃）颗粒表面吸附的多环芳烃（PAHs）与9.77 ppm二氧化氮（NO₂）的硝化反应展开系统探究。实验选用蒽、菲、芘、屈、荧蒽及苝作为模型PAHs，考察了载体表面吸附水（H₂Oads）与PAHs反应活性对硝化反应动力学及机理的影响。在吸附水含量为4.2 wt%的水合硅胶表面，反应活性最强的苝遵循准一级反应动力学进行硝化，中等活性PAHs（蒽与芘）及低活性屈则通过H⁺自催化反应完成硝化；而在吸附水含量仅0.02 wt%的干燥Fe₂O₃表面，中等活性PAHs的硝化遵循准一级反应，低活性屈则通过H⁺自催化反应进行。两类载体上的实验结果均显示，随着PAHs反应活性降低，其硝化反应均由准一级反应转变为H⁺自催化反应，表明硝化反应的动力学与机理受NO₂暴露后在吸附水层中生成的H⁺浓度调控。在干燥Fe₂O₃表面，活性最强的苝与中等活性PAHs通过NO₂直接完成硝化；而在水合硅胶表面，中等活性PAHs及屈则经由NO₂⁺进行硝化——该NO₂⁺可通过NO₂与NO₂暴露后生成、且由硝化过程释放的H⁺之间的预平衡过程形成。NO₂⁺的生成路径得到两项关键证据的佐证：一是在吸附了硫酸（H₂SO₄）的水合硅胶表面观测到H⁺自催化硝化反应加速，二是已有研究在水合硼硅酸盐玻璃中检测到NO₂⁺。