Propriétés photocatalytiques des aerosols minéraux – PhotoDust

The surfaces of uplifted minerals during dust events are suggested to be photochemically active under atmospherically relevant conditions. Such photocatalytical properties may introduce so far unconsidered new chemical pathways that impact on the composition of the atmosphere. This project includes experimental (laboratory based) and theoretical (atmospheric modelling) studies of the impact of mineral dust and organics on several aspects of atmospheric / environmental science. Near-UV/vis light-absorbing species (such as TiO2, Fe2O3, FeO, MgO) present in mineral dust aerosol interacting with gas trace gases can initiate a new and potentially important photo-induced heterogeneous chemistry, which presently is almost completely undocumented in the atmosphere. The experimental tools available to the consortium enable study of kinetic and photochemical features of the interactions of trace gases with pure and organics coated mineral dust. The laboratory studies are designed to investigate the interactions of several important atmospheric trace-gases with pure and organic coated authentic (Saharan, Arizona) and synthetic airborne mineral aerosol samples under conditions which are relevant for the atmosphere ' including light (which has been so far totally neglected). In addition to traditional macro-surfaces the use of dispersed, airborne dust samples (rather than bulk substrates) will enable the physical-chemical parameters that describe the process to be transferred with a high level of confidence to the real atmosphere. The parameters obtained include uptake coefficients, reaction mechanisms, reaction products and their dependence on atmospheric variables such as relative humidity, intensity and type of irradiation and concentrations of other trace gases. The trace gases under investigation include atmospheric species that are likely to have significant impacts on the atmospheric SOx, NOy, NOx and HOx budgets and O3 mixing ratios. Furthermore, the experimental data will enable assessment of the impact of such trace-gas interactions on the optical and cloud forming properties of mineral dust (nitrate and sulphate formation). The role of mineral dust in changing concentrations of e.g. key SO2, NOx reservoirs, the HO2 / OH budgets and both direct and indirect impacts on tropospheric ozone will be assessed within a realistic framework of known gas-phase reactions and the main aerosol types (mineral dust, primary and secondary organics, black carbon, sulphate and sea-salt). In addition, the effects of chemical ageing / changing hygroscopic properties of mineral dust during transport and the associated impact on optical properties on the radiation budget will be assessed. Once improved with the new laboratory data, the models will be in a position to provide more accurate prognoses of the effects of e.g. future pollutant emissions under different dust loading scenarios.