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Airborne particle characterisation using the polarisation state of the scattered light
Abstracts years, the need for a more complete characterisation technology, particularly high speed data processing,
SID-A WING-MOUNTED OF PARTICLE SHAPE P. H. Kaye,* * Engineering
233
of particles, have resulted
in real time, coupled with rapid advances in advances on a number of fronts.
in
INSTRUMENT FOR IN SITU CLASSIFICATION AND SIZE WITHIN CLOUDS AND AEROSOLS
E. Hirst,*
S. Saunders,*
D. Johnson+
and M. Pickering’
Research & Development Centre, Univ. of Hertfordshire, ‘Meteorological Research Flight, Farnborough, U.K.
Hatfield,
U.K
This paper describes progress of the development of a new aircraft mounted instrument for use in those areas of cloud microphysics and aerosol research where particle size and shape are important parameters. Specific objectives are to facilitate discrimination between super-cooled water droplets and ice crystals of l-25 pm size within cirrus clouds, and to provide information on cloud interstitial aerosols. The new instrument will ultimately be carried in a wing pod with communication to an inboard processor for data display and logging. It is designed to achieve particle classification at throughput rates of up to 10,000 particles per second within a (spherical equivalent) particle size range from h 1 to 100pm diameter. Data are processed in real-time to ascribe size and shape (more correctly, scattering asymmetry) factors to each particle. These data are passed at 100ms intervals to the inboard processor which will both log the data (with appropriate time-stamps) and provide the observer with a simplified, continuously updated, real-time history plot of spherical and non-spherical particle concentration variations over the preceding 5min of flight time. The logged data will allow detailed post-flight analysis of temporal changes in particle size and shape spectra, the 100ms logging cycle corresponding to a 10m spatial resolution within clouds traversed at a flight speed of lOOms-‘.
AIRBORNE PARTICLE CHARACTERISATION USING THE POLARISATION STATE OF THE SCATTERED LIGHT J. M. Clark, CBD Porton
E. V. J. Foot
Down,
Salisbury,
and P. B. Withers Wiltshire,
SP4 OJQ, U.K
The scattered light pattern from particles passing through a laser beam contains valuable information about the particle’s structure and optical properties. Part of this information is encoded in the polarisation state of the scattered light. The Aerosol Detection Group, at GBD Porton Down, is investigating ways to utilise this polarisation information to characterise aerosol particles. Using a light scattering instrument developed in-house, together with recording equipment consisting of CCD cameras and a frame grabber, we have shown that spherical particles of similar dimensions but differing complex refractive indices can be readily distinguished. The polarisation state of the scattered light from three distinct types of particle (transparent spheres, highly absorbing carbon, and metals) has been studied and the results agree with theoretical predictions. Initial results from non-spherical particles are also described.
LENGTH-CLASSIFICATION OF FIBROUS AEROSOLS USING A DIELECTROPHORETIC CLASSIFIER A. D. Maynard,*
P. A. Baron+ and G. Deyet
*Health and Safety Laboratory, ‘National
Institute
for Occupational
Broad Lane, Sheffield, U.K. Safety and Health, Cincinnat. OH U.S.A.
Work has been in progress for some time at the National Institute for Occupational Safety (NIOSH) on a device for classifying airborne fibres in terms of their length. A similar device has now been assembled at the Heath and Safety Laboratory, and is currently under development. This system has been designed to be fully controlled from a PC, thus giving it a degree of flexibility in how it is set up and operated. Preliminary results from sampling a polydisperse fibrous aerosol show the classifier to be able to provide relatively narrow fibre length distributions. At present fine fibres are ingressing into the classified fibre sample, and fibre distributions from the classifier’s output are broader than those from instruments at NIOSH. If these problems are overcome the system looks promising for both measuring the length distribution of fibrous aerosols and generating length-monodisperse fibre samples.
SID-A WING-MOUNTED OF PARTICLE SHAPE P. H. Kaye,* * Engineering
233
of particles, have resulted
in real time, coupled with rapid advances in advances on a number of fronts.
in
INSTRUMENT FOR IN SITU CLASSIFICATION AND SIZE WITHIN CLOUDS AND AEROSOLS
E. Hirst,*
S. Saunders,*
D. Johnson+
and M. Pickering’
Research & Development Centre, Univ. of Hertfordshire, ‘Meteorological Research Flight, Farnborough, U.K.
Hatfield,
U.K
This paper describes progress of the development of a new aircraft mounted instrument for use in those areas of cloud microphysics and aerosol research where particle size and shape are important parameters. Specific objectives are to facilitate discrimination between super-cooled water droplets and ice crystals of l-25 pm size within cirrus clouds, and to provide information on cloud interstitial aerosols. The new instrument will ultimately be carried in a wing pod with communication to an inboard processor for data display and logging. It is designed to achieve particle classification at throughput rates of up to 10,000 particles per second within a (spherical equivalent) particle size range from h 1 to 100pm diameter. Data are processed in real-time to ascribe size and shape (more correctly, scattering asymmetry) factors to each particle. These data are passed at 100ms intervals to the inboard processor which will both log the data (with appropriate time-stamps) and provide the observer with a simplified, continuously updated, real-time history plot of spherical and non-spherical particle concentration variations over the preceding 5min of flight time. The logged data will allow detailed post-flight analysis of temporal changes in particle size and shape spectra, the 100ms logging cycle corresponding to a 10m spatial resolution within clouds traversed at a flight speed of lOOms-‘.
AIRBORNE PARTICLE CHARACTERISATION USING THE POLARISATION STATE OF THE SCATTERED LIGHT J. M. Clark, CBD Porton
E. V. J. Foot
Down,
Salisbury,
and P. B. Withers Wiltshire,
SP4 OJQ, U.K
The scattered light pattern from particles passing through a laser beam contains valuable information about the particle’s structure and optical properties. Part of this information is encoded in the polarisation state of the scattered light. The Aerosol Detection Group, at GBD Porton Down, is investigating ways to utilise this polarisation information to characterise aerosol particles. Using a light scattering instrument developed in-house, together with recording equipment consisting of CCD cameras and a frame grabber, we have shown that spherical particles of similar dimensions but differing complex refractive indices can be readily distinguished. The polarisation state of the scattered light from three distinct types of particle (transparent spheres, highly absorbing carbon, and metals) has been studied and the results agree with theoretical predictions. Initial results from non-spherical particles are also described.
LENGTH-CLASSIFICATION OF FIBROUS AEROSOLS USING A DIELECTROPHORETIC CLASSIFIER A. D. Maynard,*
P. A. Baron+ and G. Deyet
*Health and Safety Laboratory, ‘National
Institute
for Occupational
Broad Lane, Sheffield, U.K. Safety and Health, Cincinnat. OH U.S.A.
Work has been in progress for some time at the National Institute for Occupational Safety (NIOSH) on a device for classifying airborne fibres in terms of their length. A similar device has now been assembled at the Heath and Safety Laboratory, and is currently under development. This system has been designed to be fully controlled from a PC, thus giving it a degree of flexibility in how it is set up and operated. Preliminary results from sampling a polydisperse fibrous aerosol show the classifier to be able to provide relatively narrow fibre length distributions. At present fine fibres are ingressing into the classified fibre sample, and fibre distributions from the classifier’s output are broader than those from instruments at NIOSH. If these problems are overcome the system looks promising for both measuring the length distribution of fibrous aerosols and generating length-monodisperse fibre samples.