AbstractsChemistry

This doctoral work aims at an enhanced understanding of the complex links and feedbacks between natural and anthropogenic pollutants and the radiation-cloud-precipitation cycle in the atmosphere, through direct, semi-direct and indirect interactions. For this scope the development of a proper modelling tool was necessary in order to use it for the coupled simulation of these physical and chemical processes. For this purpose the Regional Atmospheric Modeling System (RAMS) has been extended with gas, aqueous and aerosol phase chemical mechanisms, online photolysis component, biogenic and anthropogenic emissions and a new radiation scheme. The aerosols from the natural and anthropogenic activities have been linked with the radiation and microphysical processes in order to address issues related to their interaction with the radiation budget, cloud properties, precipitation and, consequently, photolytic reaction and chemical processes. The new integrated model is named RAMS/ICLAMS (Regional Atmospheric Modeling System/Integrated Community Limited Area Modeling System). The main results from the application of the model revealed the complex nature of the paths of interaction between the different atmospheric processes. The simulations with and without aerosol impacts showed the contribution of the direct and indirect mechanisms in the atmosphere. Through these mechanisms the alteration of radiation fluxes influences meteorology (temperature, surface fluxes, clouds etc.) and chemistry (photochemical processes, temperature dependent reactions, pollutant advection and diffusion). The effect of aerosols was projected in a linear way on shortwave radiation and a non-linear way on long-wave radiation. Terrestrial upwelling longwave radiation showed a complex daytime behavior, showing both enhancement and attenuation areas. The results indicated that the vertical structure of the dust layer governs the magnitude of feedback on radiation. Sea salt particles also reduce surface shortwave radiation and increase downwelling longwave radiation. The activation of natural particles as CCN causes small changes in radiation fluxes and temperature, however, precipitation is influenced more by the indirect than by the direct and semi-direct effects. The total precipitation of a cloud system is not affected by the presence of the additional CCN but its spatiotemporal characteristics are altered when taking or not taking into account the feedback mechanisms. The inclusion of aerosol radiative effects leads to improved performance of the model regarding both meteorological and air quality parameters.The simulations with the online model gave more accurate results, for ozone and sulphate aerosols, compared to the offline approach (represented by an offline chemical transport model). These results indicate that coupled simulation can add to the accuracy of the model. Apart from the avoidance of interpolation between models (since in the online approach all processes are simulated in the same spatiotemporal configuration), the improvement can be…