Surface-enhanced nitrate photolysis on ice.
نویسندگان
چکیده
Heterogeneous nitrate photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole-forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproduct yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air-ice interface within the snowpack suppresses the diffusive uptake kinetics, thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied, providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ∼3-fold enhancement in photolysis rates to be correlated with the nitrates' distorted intramolecular geometry, thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than that in the bulk. A simple 1D kinetic model suggests (1) that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO2 emissions from a 5(8) nm thick photochemically active interfacial layer by 30(60)%, and (2) that 25(40)% of the NO2 photochemical emissions to the snowpack interstitial air are released from the topmost molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface.
منابع مشابه
Nitrate photolysis on ice surfaces
Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion EGU Abstract Nitrate photolysis in the wavelength range 250–1200 nm was studied on ice in a controlled laboratory experiment. Monolayer coverage of nitrate was achieved by dosing w...
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ورودعنوان ژورنال:
- The journal of physical chemistry. A
دوره 119 10 شماره
صفحات -
تاریخ انتشار 2015