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The article provides information on the photochemistry of adsorbed nitrate which is monitored with transmission Fourier Transform Infrared (FTIR) spectroscopy by using nitric acid-reacted alumina. It states that adsorbed nitrate undergoes photochemical reaction to yield several gas-phase products and coadsorbed water and molecular oxygen. It discusses the photolysis time function and gas-phase product distribution followed by broadband irradiation.

The surface photochemistry of nitrate,formed from nitric acidadsorption, on hematite (α-Fe2O3) particlesurfaces under different environmental conditions is investigatedusing X-ray photoelectron spectroscopy (XPS). Following exposure ofα-Fe2O3particle surfaces to gas-phasenitric acid, a peak in the N1s region is seen at 407.4 eV; this bindingenergy is indicative of adsorbed nitrate. Upon broadband irradiationwith light (λ > 300 nm), the nitrate peak decreases in intensityas a result of a decrease in adsorbed nitrate on the surface. Concomitantwith this decrease in the nitrate coverage, there is the appearanceof two lower binding energy peaks in the N1s region at 401.7 and 400.3eV, due to reduced nitrogen species. The formation as well as thestability of these reduced nitrogen species, identified as NO–and N–, are further investigatedas a function of water vapor pressure. Additionally, irradiation ofadsorbed nitrate on α-Fe2O3generatesthree nitrogen gas-phase products including NO2, NO, andN2O. As shown here, different environmental conditionsof water vapor pressure and the presence of molecular oxygen greatlyinfluence the relative photoproduct distribution from nitrate surfacephotochemistry. The atmospheric implications of these results arediscussed. [ABSTRACT FROM AUTHOR]

Abstract A large part of oceanic biological production is limited by the scarcity of dissolved iron. Mineral dust aerosol, processed under acidic atmospheric conditions, is the primary natural source of bioavailable iron to oceanic life. However, synergistic and antagonistic effects of non-Fe-containing minerals on atmospheric processing of Fe-containing minerals and Fe solubilization are poorly understood. The current study focuses on mineralogical influences of non-Fe-bearing semiconductor minerals, such as titanium dioxide (TiO 2), on the dissolution of iron in selected natural mineral dust aerosols under atmospherically relevant conditions. Further, the role of elevated Ti concentrations in dust is evaluated using magnetite, a proxy for Fe(II) containing minerals, under both dark and light conditions. Our results highlight that relatively higher Ti:Fe ratios, regardless of their total Fe content, enhances the total iron dissolution in mineral dust aerosols as well as in magnetite. Moreover, elevated Ti percentages also yield high Fe(II) fractions in mineral dust systems under dark conditions. Upon irradiation however, dissolved Fe(II) is suppressed by high Ti levels due to the involvement of photochemical redox cycling reactions with hydroxyl radicals (•OH). These synergistic and antagonistic effects of Ti are further evaluated by altering the chemical composition of natural dusts with artificially added anatase (TiO 2) and synthetic amorphous titania. The current study reveals important mineralogical controls by non-Fe-bearing minerals on dust iron dissolution to better understand global iron mobilization. Graphical abstract Image 1 Highlights • TiO 2 in natural mineral-dust enhances bioavailable iron production. • TiO 2 boosts dissolved Fe(II) fraction during night but suppress in daytime. • Above effects of TiO 2 persists with amorphous titania. • Magnetite in dust decreases the Fe(II) production during the daytime. [ABSTRACT FROM AUTHOR]

Under acidic atmospheric conditions, iron leached from atmospheric mineral dust may influence the distribution of bioavailable iron at a global scale. However, the effects of non-Fe-containing minerals on iron dissolution remain unknown. This work describes metal-metal synergistic and antagonistic effects on iron dissolution that go beyond aggregation and ionic strength effects in mineral dust mixtures. In this study, we investigated iron mobilization by proton-promoted dissolution in natural mineral dust samples from the Kalahari Desert (SZ1) and Australian Red Dawn event (RO), along with one iron oxide proxy, hematite. The total iron dissolution in natural dust samples highly corresponds with the respective amount of Ti, rather than their particle sizes or Fe contents. The dust sample with high Ti content, SZ1, also showed a higher fraction of dissolved Fe(II), under dark conditions. These observations are in good agreement with the dissolution data for hematite artificially mixed with metal oxides. Total iron dissolution in hematite, mixed with TiO 2 , is 1.5- and 2-fold higher compared to that of just hematite under dark and light conditions, respectively. However, dissolution of hematite is suppressed when mixed with Al 2 O 3 and CaO. Under dark conditions, furthermore, dissolved Fe(II) fraction is enhanced for hematite when mixed with TiO 2 compared to that of other mixtures or hematite alone. Yet, dissolved Fe(II) is lower in hematite mixed with TiO 2 under light conditions compared to that of hematite alone, suggesting photo-oxidation of Fe(II) by reactive oxygen species, such as OH radicals. [ABSTRACT FROM AUTHOR]