Titanium dioxide (TiO₂) is extensively used with the process of urbanization and potentially influences atmospheric chemistry, which is yet unclear. In this work, we demonstrated strong production of Cl₂ from illuminated KCl-coated TiO₂ membranes and suggested an important daytime source of chlorine radicals. We found that water and oxygen were required for the reactions to proceed, and Cl₂ production increased linearly with the amount of coated KCl, humidity of the carrier gas, and light intensity. These results suggested that water promotes the reactivity of coated KCl via interaction with the crystal lattice to release free chloride ions (Cl^–). The free Cl^– transfer charges to O₂ via photoactivated TiO₂ to form Cl₂ and probably the O₂^– radical. In addition to Cl₂, ClO and HOCl were also observed via the complex reactions between Cl/Cl₂ and HO_x. An intensive campaign was conducted in Shanghai, during which evident daytime peaks of Cl₂ were observed. Estimated Cl₂ production from TiO₂ photocatalysis can be up to 0.2 ppb/h when the TiO₂-containing surface reaches 20% of the urban surface, and highly correlated to the observed Cl₂. Our results suggest a non-negligible role of TiO₂ in atmospheric photochemistry via altering the radical budget.

中文翻译：

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从含氯化物的二氧化钛表面光诱导生产氯分子

二氧化钛（TiO ₂）在城市化过程中被广泛使用，并可能影响大气化学，目前尚不清楚。在这项工作中，我们证明了从照明的KCl涂层TiO ₂膜可大量生产Cl ₂，并提出了白天重要的氯自由基来源。我们发现，进行反应需要水和氧气，Cl _2的生成量随被覆KCl的量，载气的湿度和光强度线性增加。这些结果表明，水经由与晶格释放游离氯离子（CL相互作用促进涂布的KCl的反应性^- ）。免费的Cl ^–转移至O的费用₂通过光活化的TiO ₂，以形成氯₂和可能是Ò ₂ ^-基团。除了Cl _2以外，还通过Cl / Cl ₂和HO _x之间的复杂反应观察到ClO和HOCl 。在上海进行了一次密集运动，在此期间观察到明显的白天Cl ₂高峰。当含TiO ₂的表面达到城市表面的20％时，估计的TiO ₂光催化生产的Cl ₂可以高达0.2 ppb / h ，并且与观察到的Cl ₂高度相关。我们的结果表明TiO _2的作用不可忽略 通过改变自由基的预算来进行大气光化学反应。