Das Projekt "Entwicklung eines kompakten transportablen Instruments fuer die Messung von OH und HO2 in der Troposhaere auf abgesetzten und luftgestuetzten Plattformen" wird vom Umweltbundesamt gefördert und von Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre durchgeführt. 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 "Laboruntersuchungen zur Kinetik stratosphaerisch relevanter Reaktionen von BRO- und IO-Radikalen" wird vom Umweltbundesamt gefördert und von Universität-Gesamthochschule Essen, Fachbereich 8 Chemie, Institut für Physikalische und Theoretische Chemie durchgeführt. Fuer die og Untersuchungen ist geplant, eine kombinierte LIF/UV-VIS-Absorptions-Anordnung aufzubauen. Die Erzeugung der verschiedenen Radikale soll durch Excimer-Laserphotolyse geeigneter Radikalvorlaeufer erfolgen. IO-Radikale koennen sehr empfindlich mit Hilfe der Laser-induzierten Fluoreszens-(LIF)-Technik nachgewiesen werden. Die Anregung erfolgt dabei im A2II3/2 (v'=2) kleiner -- X2II3/2 (v''=0) - Uebergang mit Fluoreszenz aus v'' = 3. BrO bzw CIO-Radikale besitzen ausgepraegte UV-Bandenspektren mit relativ grossen Absorptionskoeffizienten im nahen UV. Damit ist es moeglich, diese Spezies durch zeitaufgeloeste UV-Absorptionsspektroskopie zu detektieren. Durch Einsatz einer 'gatebaren' CCD-Kamera wird erreicht, dass die Absorption der Edukte (CI2, Br2 etc) separiert werden koennen.