Gaseous nitrous acid (HONO) has the potential to greatly contribute to the atmospheric oxidation capacity. Increased attention has been paid to in-particle nitrite or nitrous acid, N(III), as one of the HONO sources. However, sources and formation mechanisms of N(III) remain uncertain. Here, we study a much less examined reaction of Fe(II) and nitrate as a source of N(III). The N(III) production was indirectly probed by its multiphase reaction with SO₂ for sulfate production. Particles containing nitrate and Fe(III) were irradiated for generating Fe(II). Sulfate production was enhanced by the presence of UV and organic compounds likely because of the enhanced redox cycle between Fe(II) and Fe(III). Sulfate production rate increases with the concentration of iron–organic complexes in nitrate particles. Similarly, higher concentrations of iron–organic complexes yield higher nitrate decay rates. The estimated production rates of N(III) under simulated conditions in our study vary from 0.1 to 3.0 μg m^–3 of air h^–1. These values are comparable to HONO production rates of 0.2–1.6 ppbv h^–1, which fall in the values reported in laboratory and field studies. The present study highlights a synergistic effect of the coexistence of iron–organic complexes and nitrate under irradiation as a source of N(III).

中文翻译：

---

铁-有机配合物光解促进硝酸盐和Fe(II)反应生成亚硝酸盐/亚硝酸

气态亚硝酸 (HONO) 具有极大地促进大气氧化能力的潜力。作为 HONO 来源之一的颗粒内亚硝酸盐或亚硝酸 N(III) 受到越来越多的关注。然而，N(III) 的来源和形成机制仍不确定。在这里，我们研究了作为 N(III) 来源的 Fe(II) 和硝酸盐的反应要少得多。通过与 SO _{2 的}多相反应间接探测 N(III) 的产生用于硫酸盐生产。含有硝酸盐和 Fe(III) 的粒子被辐照以生成 Fe(II)。由于 Fe(II) 和 Fe(III) 之间的氧化还原循环增强，紫外线和有机化合物的存在增强了硫酸盐的产生。硫酸盐生产速率随着硝酸盐颗粒中铁-有机复合物的浓度而增加。同样，铁-有机复合物的浓度越高，硝酸盐的衰减率也越高。在我们的研究中，模拟条件下 N(III) 的估计生产率从 0.1 到 3.0 μg m ^–3的空气 h ^–1不等。这些值与 0.2–1.6 ppbv h ^{–1 的}HONO 生产率相当，属于实验室和实地研究报告的值。本研究强调了铁有机配合物和硝酸盐在辐照下共存作为 N(III) 来源的协同效应。