Das Projekt "CLOUD" wird/wurde gefördert durch: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung. Es wird/wurde ausgeführt durch: Paul Scherrer Institut, Labor für Atmosphärenchemie.CLOUD is an acronym for Cosmics Leaving OUtdoor Droplets. CLOUD was designed to investigate the influence of galactic cosmic rays (GCRs) on ions, aerosols, cloud condensation nuclei (CCN) and clouds, with the CLOUD facility at CERN, and thereby to assess the significance of a possible ''solar indirect'' contribution to climate change. In a more general term, CLOUD aims at resolving one of the most challenging and long-standing problems in atmospheric science - to understand how new aerosol particles are formed in the atmosphere and the effect these particles have on the global atmosphere and climate. The present poor experimental understanding of aerosol nucleation and growth is preventing the inclusion of physics-based mechanisms in global models, and limiting our understanding of how a major fraction of atmospheric aerosol will influence future climate. The contribution of aerosols and clouds is recognized by the Intergovernmental Panel on Climate Change as the most important source of uncertainty in the radiative forcing of climate change, and is limiting our capability to make reliable climate projections. With the CLOUD facility at CERN we have for the first time an experimental chamber of the highest technological performance available, where the atmosphere is recreated from ultra-pure air with added water vapor, trace gases under study and, for certain experiments, aerosols. The chamber is located at the beamline (T11) at the CERN Proton Synchrotron accelerator, and is equipped with a wide range of sensitive instruments to analyze their contents via optical ports or sampling probes. The accelerator provides an adjustable and precisely measurable beam of 'cosmic rays' that closely matches natural cosmic rays in ionization density, uniformity and intensity, spanning the atmospheric range from ground level to the maximum around 15 km altitude. In contrast with experiments in the atmosphere, CLOUD will be able to compare processes when the cosmic ray beam is varied, and all experimental parameters can be precisely controlled and measured. As a result of this, CLOUD has established itself as the worlds pre-eminent experiment for these studies. Within the next 10 years, a multi-parameter experimental phase space will be mapped, involving numerous variables such as temperature, relative humidity, trace gases and their concentrations, ionization, nucleation rates, growth rates, droplet and ice particle activation, as well as liquid and ice cloud microphysics.
Das Projekt "FIRETRACC/100: Firn Record of Trace Gases Relevant to Atmospheric Chemical Change over 100 Years" wird/wurde gefördert durch: Bundesamt für Bildung und Wissenschaft. Es wird/wurde ausgeführt durch: Universität Bern, Physikalisches Institut, Abteilung für Klima- und Umweltphysik.There have been dramatic changes in the chemistry of the troposphere over the period of rapid industrialisation during this century. There is evidence that tropospheric ozone has doubled in the Northern Hemisphere in this time, and modelling studies have suggested significant changes in the ability of the atmosphere to remove pollutants (the oxidising capacity'). Direct measurements of photooxidant chemistry have, however, only been made in recent years, whilst measurements of the trace gases which drive this chemistry extend back only to the late 1970s. This project aims to use 'firn air' - air trapped in deep polar snow - to examine the record of trace gases in both the Northern and Southern hemispheres over the last 80 to 100 years. Unlike ice cores, firn extraction yields large volumes (tens of litres) of air for analysis. This allows samples to be circulated between laboratories for repeated analysis of different suites of trace gases at ultra-trace levels. This will enable a detailed picture of the atmospheric composition to be built up in air of different ages. Extensive modelling studies will then be conducted to determine the trends of short-lived reactive species such as ozone, hydroxyl radical, peroxide, formaldehyde, and reactive oxides of nitrogen. Hence we will determine the extent of human impact on the trace gas composition and photooxidant chemistry of the troposphere. In summary, the objectives of FIRETRACC/100 are as follows - To determine the global trends of trace gases relevant to tropospheric chemistry over the 20th century. These will include CO, the isotopic composition of CO, hydrocarbons, alkyl nitrates, numerous OH-reactive halocarbons (such as methyl chloride, methyl chloroform, methyl bromide, hydrochlofluorocarbons, etc.), and sulphur gases (COS, CS2, etc.). Trends of longer lived gases will also be determined for dating purposes (CO2, CFCs, SF6, perfluorocarbons, etc.) - Determine the evolution of inter-hemispheric ratios of OH-sensitive species to constrain modelled global OH fields - Examine ratios of parent hydrocarbons to alkyl nitrates to place constraints on NOX fields in models - Elucidate the sources of CO from isotopic studies and use to deconvolute CO/methane coupling in models - Reconstruct the history of ozone, OH and tropospheric oxidising capacity over the past 100 years using full chemistry 2-D models - Determine the influence of 20th century industrialisation on the gas phase composition and chemistry of the lower atmosphere.