Das Projekt "Kernbildungsprozesse durch Oxidation biogener fluechtiger organischer Verbindungen (NUCVOC)" wird vom Umweltbundesamt gefördert und von Gesellschaft zur Förderung der Spektrochemie und Angewandten Spektroskopie, Institut für Spektrochemie und Angewandte Spektroskopie durchgeführt. Atmospheric aerosol particles affect the Earth's radiative balance both directly through backscatter of solar radiation and indirectly as cloud condensation nuclei (CCN). At present, the effects of the tropospheric aerosols are one of the largest uncertainties in quantifying climate forcing due to man-made changes in the composition of the atmosphere. The main tasks covered by NUCVOC addresses two aspects with considerable tropospheric relevance: -to evaluate the formation of aerosol quantitatively from natural sources with special emphasis on new particle formation processes, -to gain information about the organic component of the tropospheric aerosol. The overall objectives of the NUCVOC projekt can be summarized as follows: Systematic investigation of the formation of particles of selected model compounds (alpha-pinene, beta-pinene, limonene, sabinene etc) in laboratory studies (considering oxidation by NOdeep3, OH, Odeep3 reactions). Chemical analysis of the organic particle phase focusing on the very non-volatile fraction of the biogenic oxidation products. Development of the chemical mechanism describing the routes to form condensable species. Experimental verification of the nucleating abilities of certain products by A) The synthesis of a few selesignificant oxidation products. B) The determination of relevant physical parameters of these compounds (surface tension, density etc). C) The use of the thermal diffusion cloud chamber. Modelling the formation of particles (homogeneous nucleation, condensation, coagulation etc) The contribution of our group will consist of following objectives: -Measuring rates of the formation of aerosol from terpenes (model compounds) reactions with NOdeep3 radicals, using time resolved techniques. NOdeep3 radicals will be generated by flash light photolysis using suitable precursor (ie HNOdeep3) and its decay in real time will be studied using laser longpath absorption. The relation of extinction of the laser light and the particle characteristics is expected to provide information on the homogeneous nucleation rates of the oxidation products. Identification of the oxidation products of biogenic VOC reactions using a photochemical smog chamber / FTIR technique. The experimental study will be accompanied by modelling studies of the homogeneous nucleation rate of oxidation products of biogenic VOC using classical nucleation theory.
Das Projekt "Modelling Heterogeneous and Homogeneous Ice Nucleation and Growth at Cirrus Cloud Levels" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Atmosphäre und Klima durchgeführt. Many aspects of the global radiation budget are now well understood. The largest remaining uncertainty is how atmospheric aerosols modify the characteristics of clouds and how that affects the global radiation budget. This project will advance the current understanding of this indirect effect for the particularly climate-relevant cirrus clouds. Cirrus clouds are high altitude clouds, formed when atmospheric water freezes into ice crystals. They reflect infrared radiation as well as sunlight and can therefore warm or cool the surface of the Earth. Atmospheric aerosols are fine solid particles or liquid droplets in the atmosphere, examples being smoke, oceanic haze or simply liquid water. Some components of aerosols affect the temperature at which water droplets freeze and are thus capable of changing the radiative properties of cirrus clouds by influencing the number and size of the clouds' ice particles. Aerosol components which reduce the freezing temperature of water impede homogeneous nucleation, that is, the process of freezing of a droplet which is not in contact with a solid particle. Other types of aerosol, such as mineral dust, raise the freezing temperature of water by providing solid surface on which ice formation can begin (heterogeneous nucleation). Cirrus clouds are an important factor for the Earth's climate. Therefore, it is crucial that their representation in climate models can account for effects induced by anthropogenic changes in the number, size and composition of aerosols in the atmosphere. The aim of this project is to develop a representation of the formation and growth of ice particles for use in climate models. Firstly, we will develop mathematical descriptions of ice nucleation and growth rates, which account for the most important aerosol types, such as mineral dust or ammonium sulfate. An existing model will allow us to determine the effect of each of the examined substances on the properties of a cirrus cloud. The chemical and aerosol input for these experiments will be taken from a state of the art aerosol - chemistry transport model, the OsloCTM2. After developing a simplified cirrus cloud model, which will be incorporated into a global model in the last stage of the project, we can determine how and to what extent the aerosol composition influences the distribution and the radiative properties of cirrus clouds on a global scale. This project will develop the first physico-chemically based representation of cirrus cloud formation for chemistry climate models (CCMs), allowing the calculation of climate effects of changes in cirrus coverage due to anthropogenic modification of atmospheric aerosols.