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Characterising aerosol particles using spatial light scattering.
J. Aerosol Sci. Vol. 29,
Suppl.I. pp.S407-S408.
1998
0 1998 Published by Elsevier Science Ltd. All rights reserved
Pergamon
Printed in Great Britain 0021~8502/98
CHARACTERISINGAEROSOLPARTICLESUSINGSPATIAL
$19.00 + 0.00
LIGHTSCATTERING.
C. M. Inman and D. J. Lewis Bristol Industrial & Research Associates Limited (BIRAL), Portishead, Science & Technology Research Centre (STRC), Univ. of Hertfordshire,
Bristol, U.K. Hatfield, U.K.
KEYWORDS Particle sizing; Particle shape; Particle asymmetry;
Laser light scattering.
The characterisation of individual aerosol particles by their size and shape is a method of identieing particles of a specific type against an ambient background. Previously, the most common method of measuring particle shape has involved collecting filter samples, which are subsequently examined by optical, or electron microscopy. The new BIRAL Aerosol Shape Analyser (ASA) uses an analysis of the spatial light distribution of light scattered by individual aerosol particles in a sample flow as a means of characterising the particles in terms of both size and shape in real-time. The new ASA is derived from the B 1010 and provides enhanced usability at a significantly reduced cost,
INSTRUMENTDESIGN Particles passing through a laser diode beam scatter light in all directions with an intensity distribution dependent on amongst other factors, the particle size and shape. Forward scattered light at angles between 8’ and 27’ is focused via a lens onto a single photomultiplier tube designated as detector channel 4. Light scattered at angles between 27’ and 140’ is incident on an ellipsoidal mirror, which refocuses the light via a spatial filter to a collimating lens assembly. The parallel light emerging from this lens assembly is therefore a 2D transform of the 3D spatial intensity distribution of light scattered by the particle and represents more than 80% of the total sphere of scattering about the particle.
PARTICLES CHAMBER
Figure
1: Schematic
DRAWN BY PUMP
THROVGH
LASER SCATTERtNG CHAMBER
diagram of the optical system of the ASA.
s407
ELECTRICALPULSESOENE~~~E~ BY tNDl”tD”AL PARTtCLE TRANSITS THROVGH LASER BEAM
S408
Abstracts
of the 5th International
Aerosol Conference
1998
This light is incident on the 3 photomultiplier tubes arranged symmetrically about the chamber axis. These are designated as asymmetry detector channels 1. 2 and 3. Shape information can be obtained by defining an asymmetry factor Ar, which is determined by the relative magnitudes of the 3 asymmetry detector signals. Size information is obtained by arithmetically combining the output of detector 4 with that of the other 3 detectors to give a spherical equivalent size function. An arrangement of the optics appears in figure I. The new BIRAL ASA is able to achieve particle classification at throughput rates of up to 20,000 particles per second, at a sample flow rate of 1 litre per minute. The instrument is capable of characterising particles with diameters of 0.520pm. Particle data is processed in real-time to determine size and shape information for each particle. The control and particle data is passed via a custom designed PC1 interface card at 50ms intervals to a host PC, which logs the data (with appropriate time and instrument status stamps). The user is provided with a selection of periodically updated, graphical representations of the real-time size and shape information. The logged data can be replayed and further statistical analysis can be performed post-sampling. Figure 2 shows a screen shot of the instrument display.
Figure 2: Screen shot of the main real-time
display screen.
ACKNOWLEDGEMENTS The authors gratefully acknowledge the support of Prof. Paul Kaye and Dr. Edwin Hirst of University of Hertfordshire, and Paul Smith and Ian Rothwell of BIRAL. REFERENCES Buckley K., Hirst E., Kaye P H. and Saunders S. (1996). A Real-time Monitoring System for Airborne Particle Shape and Size Analysis. Journal of Geophysical Research (Atmospheres), Volume 101, Number D14, pages 19215 - 19221.
Suppl.I. pp.S407-S408.
1998
0 1998 Published by Elsevier Science Ltd. All rights reserved
Pergamon
Printed in Great Britain 0021~8502/98
CHARACTERISINGAEROSOLPARTICLESUSINGSPATIAL
$19.00 + 0.00
LIGHTSCATTERING.
C. M. Inman and D. J. Lewis Bristol Industrial & Research Associates Limited (BIRAL), Portishead, Science & Technology Research Centre (STRC), Univ. of Hertfordshire,
Bristol, U.K. Hatfield, U.K.
KEYWORDS Particle sizing; Particle shape; Particle asymmetry;
Laser light scattering.
The characterisation of individual aerosol particles by their size and shape is a method of identieing particles of a specific type against an ambient background. Previously, the most common method of measuring particle shape has involved collecting filter samples, which are subsequently examined by optical, or electron microscopy. The new BIRAL Aerosol Shape Analyser (ASA) uses an analysis of the spatial light distribution of light scattered by individual aerosol particles in a sample flow as a means of characterising the particles in terms of both size and shape in real-time. The new ASA is derived from the B 1010 and provides enhanced usability at a significantly reduced cost,
INSTRUMENTDESIGN Particles passing through a laser diode beam scatter light in all directions with an intensity distribution dependent on amongst other factors, the particle size and shape. Forward scattered light at angles between 8’ and 27’ is focused via a lens onto a single photomultiplier tube designated as detector channel 4. Light scattered at angles between 27’ and 140’ is incident on an ellipsoidal mirror, which refocuses the light via a spatial filter to a collimating lens assembly. The parallel light emerging from this lens assembly is therefore a 2D transform of the 3D spatial intensity distribution of light scattered by the particle and represents more than 80% of the total sphere of scattering about the particle.
PARTICLES CHAMBER
Figure
1: Schematic
DRAWN BY PUMP
THROVGH
LASER SCATTERtNG CHAMBER
diagram of the optical system of the ASA.
s407
ELECTRICALPULSESOENE~~~E~ BY tNDl”tD”AL PARTtCLE TRANSITS THROVGH LASER BEAM
S408
Abstracts
of the 5th International
Aerosol Conference
1998
This light is incident on the 3 photomultiplier tubes arranged symmetrically about the chamber axis. These are designated as asymmetry detector channels 1. 2 and 3. Shape information can be obtained by defining an asymmetry factor Ar, which is determined by the relative magnitudes of the 3 asymmetry detector signals. Size information is obtained by arithmetically combining the output of detector 4 with that of the other 3 detectors to give a spherical equivalent size function. An arrangement of the optics appears in figure I. The new BIRAL ASA is able to achieve particle classification at throughput rates of up to 20,000 particles per second, at a sample flow rate of 1 litre per minute. The instrument is capable of characterising particles with diameters of 0.520pm. Particle data is processed in real-time to determine size and shape information for each particle. The control and particle data is passed via a custom designed PC1 interface card at 50ms intervals to a host PC, which logs the data (with appropriate time and instrument status stamps). The user is provided with a selection of periodically updated, graphical representations of the real-time size and shape information. The logged data can be replayed and further statistical analysis can be performed post-sampling. Figure 2 shows a screen shot of the instrument display.
Figure 2: Screen shot of the main real-time
display screen.
ACKNOWLEDGEMENTS The authors gratefully acknowledge the support of Prof. Paul Kaye and Dr. Edwin Hirst of University of Hertfordshire, and Paul Smith and Ian Rothwell of BIRAL. REFERENCES Buckley K., Hirst E., Kaye P H. and Saunders S. (1996). A Real-time Monitoring System for Airborne Particle Shape and Size Analysis. Journal of Geophysical Research (Atmospheres), Volume 101, Number D14, pages 19215 - 19221.