Search

Heterogeneous reactions on mineral aerosols remain an important subject in atmospheric chemistry because of their role in altering the properties of particles and the budget of trace gases. Yet, the role of coadsorption of trace gases onto mineral aerosols and potential synergistic effects are largely uncertain, especially synergistic effects between inorganic and organic gas-phase pollutants. In this study, synergistic effects between HCOOH and SO2 were investigated for the first time using in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that the heterogeneous reaction of HCOOH is hindered significantly by coexisting SO2. The total amount of formate decreased, whereas the total amount of sulfate was not affected during coadsorption on the surface of α-Fe2O3. Futhermore, part of the formate on the surface was catalytically decomposed to CO2 by α-Fe2O3 with the help of SO2. These results suggest a possible mechanism for the observed correlations between sulfate and carboxylate in the atmosphere.

Reactions of small cationic iron oxide clusters (Fe(2)O(4-6)(+)) with N(2) are investigated by experiments and first principle calculations. The cationic iron oxide clusters are generated by reaction of laser ablated iron plasma with O(2) in a supersonic expansion, and are reacted with N(2) in a fast flow reactor at near room temperature conditions. Cluster cations are detected by a time-of-flight mass spectrometer. The substitution reaction Fe(2)O(n)(+) + N(2) --> Fe(2)O(n-2)N(2)(+) + O(2) is observed for n = 5 but not for n = 4 and 6. Density functional theory calculations predict that the low-lying energy structures of Fe(2)O(4-6)(+) are with side-on (eta(1)-O(2)) or end-on (eta(2)-O(2)) bonded molecular oxygen unit(s). The calculations further predict that the substitution of eta(1)-O(2) and eta(2)-O(2) in Fe(2)O(4,6)(+) clusters by N(2) is exothermic and subject to negative and positive overall reaction barriers, respectively, at room temperature. We thus propose that the ground state structures of Fe(2)O(4)(+) and Fe(2)O(6)(+) contain eta(2)-O(2). In contrast, both the experiment and theory favor a eta(1)-O(2) in the ground state structure of Fe(2)O(5)(+).