A comprehensive kinetic study of a potential daytime nitrous acid (HONO) source reaction, the photoenhanced reduction reaction of the nitrogen dioxide (NO2) on acidic humic acid (HA), was completed using a wetted-wall flow tube (WWFT) (Fickert et al.: J. Phys. Chem. A. 102, 10689, 1998) photoreactor integrated with a high sensitivity HONO analyser (Wall et al.: J. Atmos. Chem. 55, 31–54, 2006; Huang et al.: Atmos. Environ. 36, 2225–2235, 2002). The nature of this reaction, is of great interest since recently observed, unpredictably high HONO daytime concentrations demand its ordinarily proposed heterogeneous source to proceed 60 times more rapidly at noon than during the night (Kleffmann et al.: ChemPhysChem 8, 1137–1144, 2007). This study investigated the nature of the reduction reaction with simulated colloidal HA aqueous solutions characteristic of anaerobic environmental conditions, varying in acidity, concentration and composition. Typical urban NO2 levels were investigated. Increasing photoenhanced HONO production with weakening solution acidity was detected due to increased deprotonation of the carboxyl groups within the humic acid. It was deduced that the acidic HA substrate contains numerous feasible chromophoric sensitizer units capable of photochemically reducing NO2 to HONO, owing to its ‘biofilm’ (Donlan, 2002) function under UV exposure. The mechanism was found to be more effective for HA standards with higher levels of ‘bioactivity’ (refractivity). Using a complex mathematical model developed, incorporating both chemistry and diffusion, reaction probability datasets were produced from the experimental data, providing evidence that this is, indeed, an environmentally important daytime HONO surface source reaction. The parameters required to scale up the data of the photoreactor to that of a regional rural/urban scale were assessed.

中文翻译：

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勘误表：酸性腐植酸 (HA) 水溶液吸收二氧化氮 (NO2) 作为白天缺失的亚硝酸 (HONO) 表面源

使用湿壁流管 (WWFT) (Fickert et al.: J. Phys. Chem. A. 102, 10689, 1998) 与高灵敏度 HONO 分析仪集成的光反应器（Wall 等人：J. Atmos. Chem. 55, 31-54, 2006; Huang 等人：大气环境。36, 2225–2235, 2002)。这种反应的性质引起了极大的兴趣，因为最近观察到，不可预测的高 HONO 白天浓度要求其通常提出的异质来源在中午比夜间进行的速度快 60 倍（Kleffmann 等人：ChemPhysChem 8, 1137–1144 2007）。本研究调查了具有厌氧环境条件的模拟胶体 HA 水溶液的还原反应性质，其酸度、浓度和组成各不相同。调查了典型的城市二氧化氮水平。由于腐植酸中羧基的去质子化增加，检测到光增强的 HONO 产量随着溶液酸度的减弱而增加。据推断，酸性 HA 底物包含许多可行的发色敏化剂单元，能够将 NO2 光化学还原为 HONO，这是由于其在紫外线照射下的“生物膜”（Donlan，2002）功能。发现该机制对于具有更高“生物活性”（折光率）水平的 HA 标准更有效。使用开发的复杂数学模型，结合化学和扩散，反应概率数据集是从实验数据中产生的，提供了证据表明这确实是环境重要的白天 HONO 表面源反应。评估了将光反应器的数据按比例放大到区域农村/城市规模所需的参数。