Gas-phase nitrous acid (HONO) is a major precursor of hydroxyl radicals that dominate atmospheric oxidizing capacity. Nevertheless, pathways of HONO formation remain to be explored. This study unveiled an important CO₂-catalysis mechanism of HONO formation, using Born–Oppenheimer molecular dynamics simulations and free-energy samplings. In the mechanism, HCO₃^– formed from CO₂ hydrolysis reacts with NO₂ dimers to produce HONO at water surfaces, and simultaneously, itself reconverts back to CO₂ via intermediates OC(O)ONO^– and HOC(O)ONO. A flow system experiment was performed to confirm the new mechanism, which indicated that HONO concentrations with CO₂ injections were increased by 29.4–68.5%. The new mechanism can be extended to other humid surfaces. Therefore, this study unveiled a previously overlooked vital role of CO₂ that catalyzes formation of HONO and affects atmospheric oxidizing capacity.

中文翻译：

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CO2催化异相生成HONO

气相亚硝酸 (HONO) 是主导大气氧化能力的羟基自由基的主要前体。尽管如此，HONO 的形成途径仍有待探索。该研究使用Born-Oppenheimer 分子动力学模拟和自由能采样揭示了HONO 形成的重要CO ₂催化机制。在该机构中，HCO ₃ ^-从CO形成₂与NO水解发生反应₂二聚体在水表面产生HONO，同时，本身重新转换回CO ₂经由中间体OC（O）ONO ^-和HOC（O）ONO。进行了流动系统实验以确认新机制，这表明 HONO 浓度与 CO ₂注射量增加了 29.4-68.5%。新机制可以扩展到其他潮湿的表面。因此，这项研究揭示了先前被忽视的 CO _{2 的}重要作用，它催化 HONO 的形成并影响大气氧化能力。