State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Chinese Academy of Meteorological Sciences, Beijing 100081, China.
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong 999077, China.
Environ Sci Technol. 2020 Oct 6;54(19):11848-11856. doi: 10.1021/acs.est.0c05071. Epub 2020 Sep 16.
The NO-NO cycle determines the formation of O and hence plays a critical role in the oxidizing capacity of troposphere. Traditional view concluded that the heterogeneous oxidation of NO to NO was negligible due to the weak reactivity of NO on aerosols, compared to the homogeneous oxidation process. However, the results here reported for the first time that SO can greatly promote the heterogeneous transformation of NO into NO and HONO on MgO particles under ambient conditions. The uptake coefficients of NO were increased by 2-3 orders of magnitudes on SO-aged MgO, compared to the fresh sample. Based on spectroscopic characterization and density functional theory (DFT) calculations, the active sites for the adsorption and oxidation of NO were determined to be sulfates, where an intermediate [SO-NO] complex was formed during the adsorption. The decomposition of this species led to the formation of NO and the change of sulfate configuration. The formed NO could further react with surface sulfite to form HONO and sulfate. The conversion of NO to NO and HONO on the SO-aged MgO surface under ambient conditions contributes a new formation pathway of NO and HONO and could be quite helpful for understanding the source of atmospheric oxidizing capacity as well as the formation of air pollution complexes in polluted regions such as the northern China.
NO-NO 循环决定了 O 的形成，因此在对流层的氧化能力中起着关键作用。传统观点认为，由于与均相氧化过程相比，NO 在气溶胶上的反应性较弱，因此将 NO 异相氧化为 NO 的过程可以忽略不计。然而，这里首次报道的结果表明，在环境条件下，SO 可以大大促进 MgO 颗粒上 NO 向 NO 和 HONO 的异相转化。与新鲜样品相比，SO 老化的 MgO 上的 NO 吸收系数增加了 2-3 个数量级。基于光谱特征和密度泛函理论（DFT）计算，确定了用于吸附和氧化 NO 的活性位为硫酸盐，其中在吸附过程中形成了中间[SO-NO]络合物。该物质的分解导致 NO 的形成和硫酸盐构型的变化。在环境条件下，SO 老化的 MgO 表面上 NO 向 NO 和 HONO 的转化形成了一种新的 NO 和 HONO 形成途径，这对于理解大气氧化能力的来源以及在污染地区（如中国北方）形成空气污染复合物非常有帮助。
