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FP5

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Project ID: EVK2-CT-2001-00114
Financé au titre de: FP5-EESD
Pays: Spain

Experimental mechanism validation

The detailed and simplified degradation schemes developed from the laboratory investigations have been validated using the outdoor EUPHORE smog chamber facility in Valencia, Spain.

The mechanism development can be achieved by simulating the chemical processes in an outdoor smog chamber. This has certain advantages over the use of field studies or small laboratory chambers with artificial light sources. Physical parameters like temperature, relative humidity and solar light intensity can be controlled and meteorological effects can be eliminated, thus greatly simplifying in most cases the interpretation of the data obtained during the photochemical experiments. The smog chamber facility at Valencia consists of two large (200 m3) outdoor chambers, equipped with a range of analytical methods. In situ concentration measurements are made using FTIR and UV-visible spectrometers fitted with multiple pass optical systems (path length 300-500m).

The chambers are fitted with ports for withdrawing samples for analysis by gas chromatography coupled mass spectrometry. Continuous sampling of NO, NO2 and O3 is also possible. The degradation studies of individual oxygenated VOCs can be carried out at sub-ppm levels of reactants with a minimum of interference from heterogeneous reactions at the chamber walls. It cannot be necessarily assumed that models developed under urban conditions with high NOx concentrations can be satisfactorily applied for cleaner areas with respect to the NOx content. The environmental chamber allows to work at ambient levels with respect to the reactive nitrogen oxides concentrations thus it is possible to evaluate mechanisms under the low NOx concentrations as found in rural and downwind of urban areas.

Work using these large chambers has been directed at testing the detailed degradation mechanism derived for single oxygenated compounds from laboratory data. The results allowed optimisation of unknown parameters and feedback to the laboratory studies and they have been used to validate degradation schemes for all the generic oxygenated compounds investigated. Aerosol size and number distribution will be measured during the photosmog runs using a scanning mobility particle sizer SMPS connected to a condensation nuclei counter (CNC).

The major results are quality controlled concentration-time series of reactants and products and physical parameters like humidity, temperature and spectral resolved solar light intensity obtained during the photochemical degradation of individual oxygenated compounds applicable to validate mechanisms for atmospheric conditions. Aerosol size and number distribution for individual simulation chamber runs.

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Contact

Wirtz CLAUS, (Scientist)
Tél.: +34-96-1318227
Fax: +34-96-1318190
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