Das Projekt "Development of a Compact Transportable Instrument for the Measurement of Tropospheric OH and HO2 on Remote and Airborne Platforms" wird/wurde gefördert durch: Kommission der Europäischen Gemeinschaften Brüssel. Es wird/wurde ausgeführt durch: Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre.Hydroxyl- (OH) radicals are the most important oxidants in the troposphere, because they control the chemical transformation of most gases released into the atmosphere. Many reactions of atmospheric compounds with OH form hydroperoxy-(H02) radicals which react with O3 and NO to recycle OH. This HOx cycling is a key process in the photochemistry of the troposphere, because it increases the oxidation efficiency of OH and controls the rate of formation of photooxidants (O3, H2O2, PAN, etc) in the polluted troposphere. Thus a thorough understanding of the chemistry of the HOx family is crucial to assess possible changes in the self-cleaning efficiency of the atmosphere and to understand the photochemical ozone formation in both the planetary boundary layer and in the free troposphere. Measurements of OH and HO2 are indispensable to test the existing atmospheric chemistry models; however reliable data are scarce and have only been measured from locations at ground. The instrument will be based on the laser induced fluorescence (LIF) technique which has been developed successfully in a previous EC project (Hofzumahaus and Webb, 1995) for the detection of tropospheric OH. The specific tasks of the project aim: 1) To expand the measurement capabilities of the OH LIF technique by the development of a measurement channel for HO2 radicals, in order to allow the true simultaneous measurement of OH, HO2, and of the ratio of OH/HO2, 2) To develop a compact laser system which can be operated on board on airplane and to downsize the whole LIF instrument into a compact automatizated package, 3) To improve the LIF detection sensitivity (below 105 molecules per cm3) and to reduce the measurement time for daytime OH concentrations to a few seconds. To carry out ground-based field measurements to test the new technical developments and to participate in a field campaign to measure the abundance of OH and HO2, study their natural variability, and their photochemical response time to rapid variations in atmospheric parameters. This project aims to improve our understanding of the fast photochemistry playing a role in the regional and global troposphere. In particular, it is expected that the LIF technique will be sufficiently developed by the end of the project so that airborne measurements of OH and HO2 can be realized subsequently.
Das Projekt "Chemical Composition and Processes in Clouds and Fogs: Dependence on the Size of Particles and Droplets" wird/wurde gefördert durch: Kommission der Europäischen Gemeinschaften Brüssel. Es wird/wurde ausgeführt durch: Leibniz-Institut für Troposphärenforschung e.V..A ground-based cloud experiment is to be conducted in November 1994 at the field station S Pietro Capofiume in the Po Valley to study the size dependence of chemical constituents in fog drops and aerosol particles. Four tasks have been singled out: 1) The size-dependent nucleation scavenging ratio of aerosol particles to be determined from the measured distribution of activated drops, interstitial particles and their residuals, using a system of differential mobility analysers; in parallel, the concentrations of soluble inorganic components and their size distribution in aerosol particles and droplets will be measured by means of cascade impactors and chemical analysis, 2) Gas-liquid phase partitioning of NH3, SO2 and organic acids and their anions in different aqueous phase size fractions, 3) Measurements of water-soluble Fe (II), Fe (III) and soluble iron in precursor and interstitial aerosol particles and in various size fractions of the aqueous phase, preferably as a function of time for long-lasting fogs, 4) The production of NO3 and HNO2 from NOX at high humidity and during fog events to differentiate between the two night-time oxidation pathways: I) Oxidation of NO2 by O3 to form NO3/N2O5 followed by their interaction with wet particles to form HNO3 and II) the heterogeneous reaction of NO2 with the aqueous surface of haze particles and fog drops to form HNO3 and HNO2 simultaneously: this process is expected to depend on particle and drop size.
Das Projekt "CAPAC (Climate And Pollution Analysis ..)" wird/wurde gefördert durch: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung. Es wird/wurde ausgeführt durch: Universität Basel, Institut für Meteorologie, Klimatologie und Fernerkundung.the first phase of CAPAC is dedicated to the understanding of the urban energy balance in Cairo through measurements at ground stations and from satellites in space. The in situ measurements shall provide a focussed insight in carefully chosen microclimates and provide at the same time ground truth data for the satellite images, which will expand our acquired knowledge into the spatial domain.