Das Projekt "Laser Photoakustische Spektroskopie an Gasen" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Quantenelektronik, Laboratorium für Laserspektroskopie und Umweltanalytik durchgeführt. This project is aimed at the development of laser-photoacoustic spectroscopy to trace gas monitoring. Part A involves a home-made mobile CO2 laser photoacoustic system whose potential is further extended by the implementation of several new features such as the use of laser isotopes, photoacoustic Stark cell, multipass cells, etc. The regional field studies focus on VOC, ozone and ammonia monitoring in different environments. In collaboration with FAW Waedenswil the emission of key substances of fruits that are stored under different and varying atmospheres is investigated. Compounds of interest for the fermentation process include ethanol, acetaldehyde, ethyl acetate and others. The second part concerns our high-pressure CO2 laser photoacoustic setup. Thanks to the continuous, rather than only discrete, wavelength tunability and the narrow linewidth of the laser source, this device is particularly suited for the analysis of multicomponent trace gas mixtures. Furthermore, time-resolved monitoring of the generated acoustic pulses and photothermal beam deflection signals is performed. These results yield new insights into molecular relaxation processes and reaction kinetics. Leading Questions: - How versatile are laser spectroscopic detection schemes with respect to atmospheric trace gas monitoring? - Which levels of detection sensitivity and selectivity can be achieved and how do they compare with more conventional techniques? - How suitable are laser techniques for field applications? - How could novel laser developments further improve the potential for environmental sensing?
Das Projekt "COST-Action 729 - Assessing and managing nitrogen fluxes in the atmosphere-biosphere system in Europe - Assessment of nitrogen biosphere-atmosphere exchange based on novel quantum cascade laser technology" wird vom Umweltbundesamt gefördert und von Eidgenössische Materialprüfungs- und Forschungsanstalt EMPA, Air Pollution durchgeführt. In Europe, atmospheric deposition of reactive nitrogen species is one of the major threats to ecosystems. Thus, quantification of the different fluxes and their interactions is essential to provide the basis for assessment tools to combat nitrogen accumulation in the environment. This project combines a range of established concepts to determine N-flux with a highperformance technique in infrared laser spectroscopy, which is based on novel quantum cascade lasers (QCL). The spectrometer is the first world-wide field application of continuous wave QCLs without cryogenic cooling, i.e. suited for long-term applications. It is based on two lasers at 1273 cm-1 (for CH4, N2O, H2O) and 1600 cm-1 (for NO2). The system was optimized and validated in the laboratory from August 2007 to November 2007 and has then been operational at the Swiss CarboEurope and NitroEurope Grassland site near Oensingen on the Swiss plateau until Mai 2009, allowing for integrated measurements at the field scale, which are otherwise not accessible. Our analysis of eddy covariance measurements in conjunction with semi-continuous chamber flux data and continuous N2O soil profiles suggests that gross production and gross consumption of N2O are of the same order, and as consequence only a minor fraction of N2O molecules produced in the soil reaches the atmosphere (Neftel et al., Tellus, 2007). Furthermore, the detailed analysis of laboratory and field data revealed that flux measurements of trace gases which rely on spectroscopic methods may be subject to significant bias due to a small but relevant cross sensitivity to water vapour (Neftel et al., Agricultural and Forest Meteorology, 2009). This insight has been published for N2O but has since been recognized as a general effect in laser based trace gas measurements. Furthermore, a comparison of analyzers for flux measurements of CH4 has been performed using a new field setup to simulate fluxes of trace compounds that would otherwise be below the detection limit and thus difficult to validate.