J.F. Fabriès

Bioaerosol sampling by a personal rotating cup sampler CIP 10-M

High concentrations of bioaerosols containing bacterial, fungal and biotoxinic matter are encountered in many workplaces, e.g. solid waste treatment plants, waste water treatment plants and sewage networks. A personal bioaerosol sampler, the CIP 10-M (M-microbiologic), has been developed to measure worker exposure to airborne biological agents. This sampler is battery operated; it is light and easy to wear and offers full work shift autonomy. It can sample much higher concentrations than biological impactors and limits the mechanical stress on the microorganisms. Biological particles are collected in 2 ml of liquid medium inside a rotating cup fitted with radial vanes to maintain an air flow rate of 10 l min(-1) at a rotational speed of approximately 7,000 rpm. The rotating cup is made of sterilisable material. The sampled particles follow a helicoidal trajectory as they are pushed to the surface of the liquid by centrifugal force, which creates a thin vertical liquid layer. Sterile water or another collecting liquid can be used. Three particle size selectors allow health-related aerosol fractions to be sampled according to international conventions. The sampled microbiological particles can be easily recovered for counting, incubation or further biochemical analysis, e.g., for airborne endotoxins. Its physical sampling efficiency was laboratory tested and field trials were carried out in industrial waste management conditions. The results indicate satisfactory collection efficiency, whilst experimental application has demonstrated the usefulness of the CIP 10-M personal sampler for individual bioaerosol exposure monitoring.

Personal thoracic CIP10-T sampler and its static version Cathia-T

A specific version of the personal aerosol sampler CIP 10 was designed, named CIP10-T, for sampling the conventional CEN thoracic fraction. A static sampler, named CATHIA, was also designed. It uses the same sampling head, but the size selected particles are collected onto a filter. The combined particle efficiency of the aspiration slot and the selector was measured in a horizontal wind tunnel at low air velocity, close to 16 cm s-1. The flow rate of both samplers was fixed at its nominal value, i.e., 71 min-1. Two different methods were used: the former was based on the Aerodynamic Particle Sizer (TSI); the latter used the measurement of particle size distribution of the collected samples by the Coulter technique. For the CIP10-T sampler, the particle collection efficiency onto the rotating cup was also measured. For both samplers bias and accuracy maps have been calculated, following the recommendations of a new CEN standard about sampler performance. The bias does not exceed 10% in absolute value for both samplers, within a large range of particle size distribution of the total aerosol. For the CIP10-T sampler, the accuracy map exhibits a large area where the accuracy is better than 10%, corresponding for example to 4 microns < or = MMAD < or = 14 microns for GSD = 2. For the same geometric standard deviation, the accuracy is still better than 20% for 15 microns < or = MMAD < or = 21 microns. For the CATHIA-T sampler, the accuracy map can be roughly divided into two parts. The accuracy remains better than 10% for MMAD < or = 12 microns, and it remains between 10 and 20% for coarser aerosols, with 13 microns < or = MMAD < or = 20 microns, provided GSD > or = 2.

A new experimental wind tunnel facility for aerosol sampling investigations

Abstract A new experimental wind tunnel facility for aerosol sampling investigations has been built and its performance evaluated. Subsequently, an experimental methodology using a polydisperse test aerosol of glass beads to measure entry, transmission and overall sampling efficiencies has been developed and tested. The new facility is composed of a horizontal cylindrical pipe of 5 m long and 30 cm in diameter. The measurement zone is located just at the exit, allowing to take benefit of the whole cross-sectional area inside a stabilised aerosol flow. The working air velocity range is 0.5–4.5 m s−1 Air velocity and turbulence profiles are uniform within 10%. Turbulence in the working section is controlled with a square mesh grid. The test aerosol is generated by a fluidized-bed generator and dispersed into the clean air flow upstream of the horizontal part. Generated particles are within a size interval extending from a few μm to about 80 μm in aerodynamic diameter. Tests of time and space stability of the test aerosol in the working section were carried out. They have shown a reasonably uniform spatial distribution and time stability considering the size range of generated particles. The experimental method allows to obtain, simultaneously with the same technique entry, transmission, and overall sampling efficiencies of samplers from several μm up to 70 μm in particle aerodynamic diameter with a good accuracy. It is based on the measurement of the distribution of particle number concentration vs particle aerodynamic diameter of deposited and sampled aerosols in a reference probe and in the test sampler. To evaluate both the new wind tunnel facility and the methodology, measurements of the different efficiencies were achieved using a cylindrical sharp-edged thin-walled probe as a test sampler. This evaluation was performed in three steps. At first, the reproducibility of transmission efficiency measurements of the probe working in isokinetic conditions was determined. It appears fairly good between 10 and 70 μm in particle aerodynamic diameter. Then, the methodology was applied to the assessment of the aspiration efficiency of a probe working in subisokinetic conditions. Finally, a consistency test of the data was proposed and applied to our data; it consists in comparing the mass fractions of collected samples (deposited on the internal sampler walls, collected onto filters) calculated from the efficiency data and the distributions of particle concentrations, with those which are directly recovered after each experiment and weighed. This test yields an indicator of the quality of the whole efficiency data set.

Calculation of the theoretical response of an optical particle counter and its practical usefulness

Abstract The response of an optical particle counter (OPC) was modelled from the Mie theory of light scattering and the built-in parameters of the counter. The model allowed the calculation of the output signal for any spherical particle, of a given complex refractive index, on a microcomputer. It was applied to a Royco 225 instrument. The simulation required a calibration with a reference aerosol. This calibration was carried out with monodisperse spherical particles of oleic acid obtained by a vibrating orifice aerosol generator (VOAG). The experimental values of the counter response obtained with monodisperse aerosols of oleic acid and methylene blue were then compared with the results obtained from the model. It was shown that the choice of the material used for generating monodisperse particles in order to calibrate the counter was not important. Particle size distributions were measured by the OPC for two polydisperse aerosols (coal and aluminium oxide particles), by using the response curve predicted from the model and the refractive index of the material, and then compared with those measured using a Coulter counter, after aerosol sampling onto a Nuclepore membrane filter. The comparison shows that the combination of optical measurements with the calculation of the response curve of the OPC yields accurate results when particle shape is close to the sphere, and for nonspherical particles when light absorption is high.

THE USE OF A NEW STATIC DEVICE BASED ON THE COLLECTION OF THE THORACIC FRACTION FOR THE ASSESSMENT OF THE AIRBORNE CONCENTRATION OF ASBESTOS FIBRES BY TRANSMISSION ELECTRON MICROSCOPY

A new static device, the CATHIA sampling head, based on the collection of the thoracic fraction is proposed for the assessment of the airborne concentration of asbestos fibres by transmission electron microscopy. By comparison with a standard aerosol sampling head, it has been shown that this sampler reduces the total mass concentration, but does not introduce any change in the most common index used to characterize an asbestos aerosol fibre, that is the concentration of fibres with length greater than 5 microns, diameter less than 3 microns and length to diameter ratio greater than 3. The homogeneity of the deposited dust on the collection filter favours the use of this sampling head with both the indirect and direct preparation methods.