Objectif
The objectives of the work proposed will be:
to examine, and improve if necessary, the techniques for estimating the reduction of inhalation dose by staying indoors and the deposition on indoor surfaces;
to examine the influence of the surface type, for instance the importance of furniture on the deposition process;
to consider the range of measures that may be taken to alleviate indoor exposure and in particular to examine a vacuum cleaner as a tool for reduction of the indoor air pollution;
to improve models for generic and risk assessment purposes in radiation protection.
2 full scale tests of house filtration and indoor deposition have been performed using monodisperse silicon particles labelled with dysprosium. The air exchange rate was measured using silicon fluoride as a tracer gas and monitoring its decay by chromatography. 5 um dysprosium labelled silica particles were dispersed from a Palas RBG 1000 powder disperser and a fan was used for uniform distribution. Filter samples were taken at intervals, activated and analyzed by gamma spectroscopy using a germanium lithium detector and a multichannel analyzer. Measurement was done in the living room both with and without furniture in order to test the influence of the furniture on deposition.
The deposition velocity was found to be lower for the smaller particles (0.015 cm/s unfurnished and 0.017 cm/s furnished) than for the larger particles (0.024 cm/s unfurnished and 0.038 cm/s furnished). The difference seems to be smaller than expected because the particles labelled 5 um were closer to 4 um. The relatively high deposition velocities measured are probably due to high turbulence in the room caused by the experimentors during the measurements. It can be concluded that the method developed for finding deposition characteristics (deposition constant and deposition velocity) has worked very well in the experiment performed.
A technique has been developed which allows silica particles to be labelled with a neutron activatable tracer such as dysprosium or caesium. The silica particles used are available in various monodisperse size distributions. They are suitable for tracer adsorption due to their large surface area and the presence of a large number of 8 nm pores on their surfaces. For labelling, the silica particles are shaken for 24 hours in an aqueous solution of the tracer metal salt (of typical concentration 10 mg/ml), filtered and rinsed thoroughly with distilled water to remove excess metal solution. The typical uptake of metal ions is 5 mg per gram of silica in the case of dysprosium. It has been found that heating the labelled silica to 500 C overnight, followed by relabelling, increases the uptake of metal ions by the particles by a factor of 2.
The dysprosium labelled silica particles were used in full scale tests of house filtration and indoor deposition. A size analysis of the particles was carried out using the TSI aerodynamic particle sizer. It was found that the 1 um particles had an aerodynamic diameter (AD) close to 2 um and the AD of the 5 um particles was in fact 4 um.
In the first year, Risoe would carry out the following:
Indoor and outdoor air concentration
In a test house using cosmogenic 7Be particulate as tracer to find the indoor and outdoor air concentration, and by varying the air exchange rate to find the filtering factor and the deposition constant.
Indoor deposition
To implement the method, in collaboration with Imperial College, using monodisperse silica particulate in the test house (until now it has only been used in a small scale experiment).
Vacuum cleaner as a tool for countermeasures
Begin to investigate the efficiency of different vacuum cleaners as air filters.
In the first year Imperial College would:
obtain, from its standard supplies, samples of monodisperse silica particles in the size range 1 to 10 microns, and check the size characteristics using the Imperial College APS analyzer.
make use of Imperial College's PALAS particle dispersion generator and associated 85Kr deionising source in experiments to cross check airborne particle count against air filter measurements using stable tracers. The stable tracer techniques have been developed under contract from UK industry. These comparative experiments would be conducted in the aerosol test chamber.
confirm stable tracer labelling techniques (which have been shown to have a detection limit of 10 to 100 ng particles), using the Reactor Centre facilities.
send an assistant to Risoe for a 3 month work period to participate in indoor deposition measurement using cosmogenic aerosol and to carry out the first experiment with labelled monodisperse aerosols (probably 3 micron aerosol) using air filter techniques. Imperial College would transport labelled particle supplies, dispersion generator and related equipment to Risoe.
make use of models to assist experiment design.
At the end of the first year the participants would meet to review progress. In particular they would consider the implications of the results of the first year work programme for the continuing direction of the work in the second year. In view of this the second year programme cannot be as closely defined as the first, but the following gives some indications of potential directions. Not all aspects mentioned below could be fully explored in the second year. This research could be continued subsequently if the Programme continues.
In the second year (and beyond if appropriate) Risoe would address some or all of the following aspects:
Indoor and outdoor air concentration
Reactive (depositing) gases would be used as tracers. More houses would be investigated using 7Be as tracer.
Houses from different places in the EC would be investigated.
Indoor deposition
Full scale experiments using monodisperse silica particulate would be performed, in collaboration with Imperial College, in real houses.
Vacuum cleaner as a tool for countermeasures
Experiments in real houses will be performed and the normal vacuum cleaners used in the EC would be investigated.
In the second year Imperial College would:
participate in a wider range of full scale experiments using monodisperse aerosols covering size ranges down to l micron and up to 10 micron. This will involve about 3 months spent at Risoe and the transport and provision of the appropriate College equipment.
develop data and models, in collaboration with Risoe, that can take account of the differences in behaviour expected to be found between particles in the 1 to 10 micron range, and to disseminate the results of model studies.
Looking ahead to following years, the vital question of separating the effects of infiltration from deposition needs to be answered, as a function of particle size. Also the mean residence time of deposited material, and its resuspension and cleaning needs to be addressed; preliminary work on this has been done already using Imperial College's UV scanning system DIADEM, developed under the current CEC Programme.
Champ scientifique (EuroSciVoc)
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CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
- sciences naturelles sciences chimiques chimie inorganique métal alcalin
- ingénierie et technologie génie de l'environnement ingénierie de la pollution atmosphérique
- sciences naturelles sciences de la Terre et sciences connexes de l'environnement sciences de l'environnement pollution
- sciences naturelles sciences chimiques chimie inorganique métalloïde
- sciences naturelles sciences physiques optique spectroscopie
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ROSKILDE
Danemark
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