Abstract. Dinitrogen pentoxide (N 2 O 5 ) and nitryl chloride (ClNO 2 ) are key species in nocturnal tropospheric chemistry and have significant effects on particulate nitrate formation and the following day's photochemistry through chlorine radical production and NO x recycling upon photolysis of ClNO 2 . To better understand the roles of N 2 O 5 and ClNO 2 in the high-aerosol-loading environment of northern China, an intensive field study was carried out at a high-altitude site (Mt. Tai, 1465 m a.s.l.) in the North China Plain (NCP) during the summer of 2014. Elevated ClNO 2 plumes were frequently observed in the nocturnal residual layer with a maximum mixing ratio of 2.1 ppbv (1 min), whilst N 2 O 5 was typically present at very low levels (< 30 pptv), indicating fast heterogeneous N 2 O 5 hydrolysis. Combined analyses of chemical characteristics and backward trajectories indicated that the ClNO 2 -laden air was caused by the transport of NO xrich plumes from the coal-fired industry and power plants in the NCP. The heterogeneous N 2 O 5 uptake coefficient (γ ) and ClNO 2 yield (φ) were estimated from steady-state analysis and observed growth rate of ClNO 2 . The derived γ and φ exhibited high variability, with means of 0.061 ± 0.025 and 0.28 ± 0.24, respectively. These values are higher than those derived from previous laboratory and field studies in other regions and cannot be well characterized by model parameterizations. Fast heterogeneous N 2 O 5 reactions dominated the nocturnal NO x loss in the residual layer over this region and contributed to substantial nitrate formation of up to 17 µg m −3 . The estimated nocturnal nitrate formation rates ranged from 0.2 to 4.8 µg m −3 h −1 in various plumes, with a mean of 2.2 ± 1.4 µg m −3 h −1 . The results demonstrate the significance of heterogeneous N 2 O 5 reactivity and chlorine activation in the NCP, and their unique and universal roles in fine aerosol formation and NO x transformation, and thus their potential impacts on regional haze pollution in northern China.

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Focusing on two-dimensional (2D) Janus MoSSe monolayers, we show that simultaneously existing in-plane and out-of-plane intrinsic electric fields cause Zeeman-and Rashba-type spin splitting, respectively. In MoSSe van der Waals (vdW) structures, intrinsic electric field results in a large interlayer band offset. Therefore, large interlayer band offset, being the driving force for interlayer excitons, endows ultralong lifetimes to excitons and might dissociate excitons into free carriers. In comparison to its parent structure (i.e., MoS 2 ), MoSSe vdW structures are rather appealing for new concepts in light−electricity interconversion. In addition, the Rashba effects could be tuned by changing the interlayer distances due to the competition between the intralayer and interlayer electric field. Due to the large band offset, valley polarization relaxation is markedly reduced, promising enhanced valley polarization and ultralong valley lifetimes. As a result, MoSSe vdW structures harbor strong valley-contrasting physics, making them competitive systems to their parent structures.

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