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The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO(-) and N(-), are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed.

Nitrous oxide (N2O) is an important greenhouse gas and a primary cause of stratospheric ozone destruction. Despite its importance, there remain missing sources in the N2O budget. Here we report the formation of atmospheric nitrous oxide from the decomposition of ammonium nitrate via an abiotic mechanism that is favorable in the presence of light, relative humidity and a surface. This source of N2O is not currently accounted for in the global N2O budget. Annual production of N2O from atmospheric aerosols and surface fertilizer application over the continental United States from this abiotic pathway is estimated from results of an annual chemical transport simulation with the Community Multiscale Air Quality model (CMAQ). This pathway is projected to produce 9.3(+0.7/-5.3) Gg N2O annually over North America. N2O production by this mechanism is expected globally from both megacities and agricultural areas and may become more important under future projected changes in anthropogenic emissions.

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.