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Photon correlation spectroscopy for analysis of particle size and concentration of low concentration aerosols
0
Pergamon
J. Armsol SC;. Vol. 29. Suppl. I, pp. S107-SlOS. 1998 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021~8502/98 $19.00 + 0.00
PHOTON CORRELATION SPECTROSCOPY FOR ANALYSIS OF PARTICLE SIZE AND CONCENTRATION OF LOW CONCENTRATION AEROSOLS
E.J. NIJMAN, Delft University
A.W. WILLEMSE,
K.B. GEERSE,
J.C.M. MARIJNISSEN,
B. SCARLETT
of Technology, Particle Technology Group, Julianalaan I36,2628 The Netherlands, Tel. +3 I I5 278 4372, Fax +3 I I5 278 4452
BL, Delft.
KEYWORDS Photon Correlation
Spectroscopy,
Low Concentration
Aerosols
Photon Correlation Spectroscopy (PCS) is a fast measuring technique to determine particle size in the submicrometer region. Measurements of particle size in aerosols by using PCS are known from literature. However, the use of PCS for aerosol measurements is limited by concentration. The upper limit is determined by multiple scattering of the incident light, and the lower limit is determined by the number of particles in the measuring volume, which is the intersection between the incident and the detected laser beam. Our measurements in systems with low concentrations, however, have shown that with concentrations down to 500 particles/cm”, the particle size can still be determined (Fig. I ). With the use of high-speed signal processing, accurate autocorrelationfunctions were found. These functions could be separated into two decays, of which the first one is determined by the Brownian motion. We assume that in some cases the second decay can be used to obtain the concentration by using Poisson statistics
!O 176nm/ 0 SO1 nml
0’
0
0
0.001
0.01
l
0.1
0
0
0.
I
IO
100
number of particles in the measuring volume [#/IO” cm’] Figure
I. Ratio of the particle size as measured by PCS, to the actual particle size, for 176 nm and 501 nm latex particles in water. s107
S108
Abstracts of the 5th International Aerosol Conference 1998 600
-
500
--
400
--
300
~-
200
.-
0 l 0
0
0
0
-z ; ._ v,
100 ~~ 0
-I
0
0.005
0.01
0.015
0.02
0.025
number of particles in the measuring volume [#/I 0~” cm’]
Figure 2. Measured
size of 500 nm aerosol particles (M500).
At concentrations where the measuring volume contains down to 0.001 particles. measurements were still possible. This led to a definition of the effective measuring volume. which is many times larger than the intersection between the incident and the detected laser beam. Multiple scattering is then the only mechanism leading to the detected signal. After initial measurements done in a liquid environment, the system is now capable of measuring in aerosols, where the lower detection limit for particle size is only determined by the incident laser power. The system therefore enables determination of particle size and concentration in ambient air and other aerosol environments.
REFERENCES Van Drunen, M.A., Tuinman, I.L., Marijnissen, J.C.M., Merkus, H.G., Scarlett, B. (1994) Measurement of aerosols in a silicon nitride flame by optical fiber photon correlation spectroscopy, J. Aerosol Sci. vol. 25 No. 5, 895-908.
Pergamon
J. Armsol SC;. Vol. 29. Suppl. I, pp. S107-SlOS. 1998 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021~8502/98 $19.00 + 0.00
PHOTON CORRELATION SPECTROSCOPY FOR ANALYSIS OF PARTICLE SIZE AND CONCENTRATION OF LOW CONCENTRATION AEROSOLS
E.J. NIJMAN, Delft University
A.W. WILLEMSE,
K.B. GEERSE,
J.C.M. MARIJNISSEN,
B. SCARLETT
of Technology, Particle Technology Group, Julianalaan I36,2628 The Netherlands, Tel. +3 I I5 278 4372, Fax +3 I I5 278 4452
BL, Delft.
KEYWORDS Photon Correlation
Spectroscopy,
Low Concentration
Aerosols
Photon Correlation Spectroscopy (PCS) is a fast measuring technique to determine particle size in the submicrometer region. Measurements of particle size in aerosols by using PCS are known from literature. However, the use of PCS for aerosol measurements is limited by concentration. The upper limit is determined by multiple scattering of the incident light, and the lower limit is determined by the number of particles in the measuring volume, which is the intersection between the incident and the detected laser beam. Our measurements in systems with low concentrations, however, have shown that with concentrations down to 500 particles/cm”, the particle size can still be determined (Fig. I ). With the use of high-speed signal processing, accurate autocorrelationfunctions were found. These functions could be separated into two decays, of which the first one is determined by the Brownian motion. We assume that in some cases the second decay can be used to obtain the concentration by using Poisson statistics
!O 176nm/ 0 SO1 nml
0’
0
0
0.001
0.01
l
0.1
0
0
0.
I
IO
100
number of particles in the measuring volume [#/IO” cm’] Figure
I. Ratio of the particle size as measured by PCS, to the actual particle size, for 176 nm and 501 nm latex particles in water. s107
S108
Abstracts of the 5th International Aerosol Conference 1998 600
-
500
--
400
--
300
~-
200
.-
0 l 0
0
0
0
-z ; ._ v,
100 ~~ 0
-I
0
0.005
0.01
0.015
0.02
0.025
number of particles in the measuring volume [#/I 0~” cm’]
Figure 2. Measured
size of 500 nm aerosol particles (M500).
At concentrations where the measuring volume contains down to 0.001 particles. measurements were still possible. This led to a definition of the effective measuring volume. which is many times larger than the intersection between the incident and the detected laser beam. Multiple scattering is then the only mechanism leading to the detected signal. After initial measurements done in a liquid environment, the system is now capable of measuring in aerosols, where the lower detection limit for particle size is only determined by the incident laser power. The system therefore enables determination of particle size and concentration in ambient air and other aerosol environments.
REFERENCES Van Drunen, M.A., Tuinman, I.L., Marijnissen, J.C.M., Merkus, H.G., Scarlett, B. (1994) Measurement of aerosols in a silicon nitride flame by optical fiber photon correlation spectroscopy, J. Aerosol Sci. vol. 25 No. 5, 895-908.