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A comparison of experimental and theoretical response curves of optical particle counters
The Tenth A n n u a l Conference of the Association for Aerosol Research
361
Horvath, H. and Presle, G. (1979) Measurements of visibilities in simulated atmospheres (hydrosols) and applications to real atmospheres, Aerosol research at the Institute for Experimental Physics of the University of Vienna, Part II. Horvath, H., Gorraiz, J. and Johnson, Ch. (1982) Experimental study on the visibility in absorbing media. Sci. Tot. Era'. 23, 305. Koschmieder, H. (1924) Theorie der horizontalen Sichtweite. Beitr. z. Phys.freien Arm. 12, 33, 171. Roessler, D. M. and Faxvoc. F. R. (19811 Visibility in absorbing aerosols. Atmos. Environ. 15, 151.
A COMPARISON OF EXPERIMENTAL AND THEORETICAL CURVES OF OPTICAL PARTICLE COUNTERS
RESPONSE
J. M,~KYNEN Tampere University of Technology, Department of Electrical Engineering, Laboratory of Physics, P.O. Box 527, SF-33101 Tampere 10, Finland In this work experimental and theoretical response curves o f four commercially available single particle optical counters (Climet 250, Climet 208, Royco 218 and Royco 245) have been compared. The response of single particle optical counter depends on the properties (size, shape, refractive index) of the particle, the geometry o f the optical system, the intensity and the wavelength distribution of light in the viewing
1
-
I~"
' i/l'l/~\\\\
17 i
,,
/tJi, i I/i! I
i
"
l!/ i
0
20
\. ....
l '
R218
\
.............. R2~S
~,0
'
60
\
BO
I00 o
Fig. 184. Effective weighting functions of the scattering angle.
2
05 I
0 200
tOO
600
800
1000
Fig. 185. Effective wavelength spectra of the meters.
1200 )k (nrn)
362
Aerosols in science, medicine and technolog>
volume and the spectral sensitivity of the light detector (Cooke and Kerker, 1975). For spherical particles the theoretical response I at the size Dp and refractive index m can be expressed in the form (Pinnick er at..~ 19731
IIDp, m) = i i/.:G(O)f(;',) (i t + i=)d0d,;.,
i1~
where G(O) is the effective weighting function of the scattering angle and j(;,.} is the effective wavelength spectrum {i.e, product o f the light source emission spectrum and the sensitivity of the detector) of the meter. 1~and i: are so called Mie-intensity functions. G(O) and f(2) were calculated for each meter using the values given by M#ikynen ez aL 1982. Their normalized values are presented in Figs 184 and 185. Mie-intensity functions were calculated using the subroutines of Wiscombe (1979) modified for the computer system (Wax 11/780 computer and FPS-164 array processor) of the university Experimental response curves were measured for the ideal nonabsorbing monodisperse test particles (DOP: m = 1.485 and PSL; rn = 1.592) (M~ikynen ez aL, 1982). Theoretical and experimental curves normalized for D O P to the value 0.5 at the size 2.2 #m are presented in Figs 186 a--d (the shift of the electrical zero level of the C250 has also been corrected). Agreement between theoretical and experimental curves is quite good. As an example of absorbing particles the response was measured also for Methylene Blue particles• In this case the refractive index varies
(a)
(b) 10
100 I
R 245 10
Z
/,...
•
OOP
. /
o
PSL
1,~.."
•
MB
.f
1.0
.""
C 208
4
]-7
/~
•
OOp
~'
o
PSL
//
n
# 4
-MB
..1
7
~
#// # i i-
~.0
0.1 i 1
001
.'i
o~ ;.
I
133 I ~.55
I592 -~ ..... ~50-001, J
0001
..... ISO-O01, ....... 196 - 0 661
I
0 0001
. . . .
,,,,i
O]
. . . . . . . .
i
~0
# i •
10
0.1
100
i0
- ......
~gs-0.6s,
10
100 O~ (ym)
Op (pro)
(c)
(d)
10
IO
C 250 •
I
J
00l
. . . . . . . .
. . . . . . . .
i
'7
. . . . . .
"~,
'
......
1
R218
1
:
o PSL • .B
i
.liIJ'7/"...,,. --
~
•
DOP
o
PSL
/'&' "
-i
~../i
,
10
,!i I 0.1 m
00~
!
. . . .
133
II
.....
165-001~
I
.......
196-
00l I
I0
I0
I00 Op UJm)
33
li
........... ~ 592
.......
I I I
0001 [ 01
,
J , ii
7
2.2.:
II
066i
0 001i 01
°'I
m
I
~ 9 6 - 0661
!
" 4 I i
,,•l
. . . . . . . .
10
Fig. 1861a-d). E x p e r i m e n t a l a n d theoretical responses o i lhe OPCs.
I
~0
. . . . .
IHI
lO0 DL~ (urn)
The Tenth Annual Conference of the Association for Aerosol Research
363
remarkably as a function of wavelength. Imaginary part is large a'. the effective wavelength range of C208 and R245 and small at the wavelength range used in the R218 and C250. Egan (1982) gives for m values 1.34-0.54i at 550 nm and 1.52~).016i at 820 nm. Because the m was not known in greater detail exact calculations could not be made. The general behavour of the theoretical curves, however, agrees well with these given values. As a conclusion it can thus be said that if the optical parameters of the counter are known the response can be predicted quite accurately with the aid of theoretical calculations. It can also be seen from the figures that even such values of absorption which are common in atmospheric aerosols change the response considerably.
REFERENCES Egan, W. G. (1982) Appl. Opt. 21° 1445. Cooke, D. D. and Kerker, M. (1975) Appl. Opt. 14, 734. M~ikynen. J.. Hakulinen, J., Kivist0, T. and Lehtimiiki, M. (1982) J. Aerosol Sci. 13, 529. Pinnick, R. G.. Rosen, J. M. and Hofmann, D. J. (1973) Appl. Opt. 12, 37. Wiscombe, W. (1979) NCA R Technical Note, NCA R/TN- 140 + STR.
A HIGH
RESOLUTION ELECTRICAL SPECTROMETER
MOBILITY (MAS)
AEROSOL
A. PLOMP, H. M. TEN BRINK, H. SPOELSTRA and J. F. VAN DE VATE Netherlands Energy Research Foundation, Petten, The Netherlands INTRODUCTION Present techniques used to measure the size of suboptical particles (d < 0.1/.tin) are based on the selection of aerosol according to mobility. The disadvantage o f t b e available instruments is their low size-resolution. The low resolution of the EAA (Electrical Aerosol Analyzer, TS13030) for instance is a consequence o f the low sensitivity o f t b e method to measure the concentration of the aerosol (viz. via the determination o f the charge on the particles). Recently Hoppel (1978) used a condensation nuclei counter to measure the concentration o f aerosol classified according to electrical mobility in a differential mobility chamber. Recently TSI introduced a continuous condensation nuclei counter of a novel design. According to the specifications (Liu and Pui, 1974) this instrument seemed to be well suited to be operated for the recording of the aerosol transmitted in a commercial Differential Mobility Analyzer (TSI 3071). It will be shown in the present presentation that the new combination constitutes a true aerosol spectrometer with high resolution for particles in the range o f 0.02-1/am.
MATERIALS
AND
METHODS
The new spectrometer is a combination of a commercial D M A (Differential-electrical-MobilityAnalyzer, TSI 3071) and a C C N C (Continuous Condensation Nucleus Counter, TSI 3020). A detailed description of the C C N C can be found in the recent literature(Liu and Pui, 1974).It might be best to summarize here those featuresof the instrument which are of importance for the present application. The C C N C is capable of detecting a concentration of as low as one particlein hundred c m 3 of air.Sampling of the aerosol in the condensation chamber, which is of the diffusion type, occurs in an uninterrupted continuous flow and the flow is almost insensitive to pressure drops of up to 60 cm H20. The performance of the C C N C was checked using a calibrated E S P / E M method (Van de Vate and Plomp, 1977) and a dilution method (Raes and Plomp, 1983). Aerosol for the calibration was obtained by nebulizing and subsequently drying o f solutions of uranine and NaCI in water; in this way a polydisperse aersol, characterized by lognormal distribution (dg = 0.06 #m, ag = 1.7) was obtained. A detailed description of a DMA is found in Hoppel (1978). Hence a short resum6 of the commercial apparatus will be given here. Basically the DMA consists of a concentrical, cylindrical condensator. An aerosol stream, imbedded in a concentrical sheath of air, is lead through this condensator. The charged fraction of the aerosol is deflected if an electrical field is applied. Particles acquire terminal velocities perpendicular to the main stream according to electrical mobility. At the narrow exit slit in the central electrode a well-defined mobility fraction of the positively charged aerosol is transmitted at a given value o f the electrical field. Thus aerosol particles can be selected by varying the electrical field. A reciprocal relation between applied voltage and the electrical mobility of the selected aerosol exists of the following form:
(1)
Zs= ~
where Z s is the electrical mobility, V is the voltage difference in the condensator, Q t and Qa are the flow rates o f the total flow and aerosol stream respectively. The proportionality factor ~ has a fixed value for the DMA (McMurry, 1977). In the present application Qt equals 3.31/min and Qa 0.3 l/min and thus the relation simplifies to: l
Z s = 0.132~.
(2)
Electrical mobility of particles can be translated to actual size via the following relation: ds
fl.n.C. Zo
(lb)
361
Horvath, H. and Presle, G. (1979) Measurements of visibilities in simulated atmospheres (hydrosols) and applications to real atmospheres, Aerosol research at the Institute for Experimental Physics of the University of Vienna, Part II. Horvath, H., Gorraiz, J. and Johnson, Ch. (1982) Experimental study on the visibility in absorbing media. Sci. Tot. Era'. 23, 305. Koschmieder, H. (1924) Theorie der horizontalen Sichtweite. Beitr. z. Phys.freien Arm. 12, 33, 171. Roessler, D. M. and Faxvoc. F. R. (19811 Visibility in absorbing aerosols. Atmos. Environ. 15, 151.
A COMPARISON OF EXPERIMENTAL AND THEORETICAL CURVES OF OPTICAL PARTICLE COUNTERS
RESPONSE
J. M,~KYNEN Tampere University of Technology, Department of Electrical Engineering, Laboratory of Physics, P.O. Box 527, SF-33101 Tampere 10, Finland In this work experimental and theoretical response curves o f four commercially available single particle optical counters (Climet 250, Climet 208, Royco 218 and Royco 245) have been compared. The response of single particle optical counter depends on the properties (size, shape, refractive index) of the particle, the geometry o f the optical system, the intensity and the wavelength distribution of light in the viewing
1
-
I~"
' i/l'l/~\\\\
17 i
,,
/tJi, i I/i! I
i
"
l!/ i
0
20
\. ....
l '
R218
\
.............. R2~S
~,0
'
60
\
BO
I00 o
Fig. 184. Effective weighting functions of the scattering angle.
2
05 I
0 200
tOO
600
800
1000
Fig. 185. Effective wavelength spectra of the meters.
1200 )k (nrn)
362
Aerosols in science, medicine and technolog>
volume and the spectral sensitivity of the light detector (Cooke and Kerker, 1975). For spherical particles the theoretical response I at the size Dp and refractive index m can be expressed in the form (Pinnick er at..~ 19731
IIDp, m) = i i/.:G(O)f(;',) (i t + i=)d0d,;.,
i1~
where G(O) is the effective weighting function of the scattering angle and j(;,.} is the effective wavelength spectrum {i.e, product o f the light source emission spectrum and the sensitivity of the detector) of the meter. 1~and i: are so called Mie-intensity functions. G(O) and f(2) were calculated for each meter using the values given by M#ikynen ez aL 1982. Their normalized values are presented in Figs 184 and 185. Mie-intensity functions were calculated using the subroutines of Wiscombe (1979) modified for the computer system (Wax 11/780 computer and FPS-164 array processor) of the university Experimental response curves were measured for the ideal nonabsorbing monodisperse test particles (DOP: m = 1.485 and PSL; rn = 1.592) (M~ikynen ez aL, 1982). Theoretical and experimental curves normalized for D O P to the value 0.5 at the size 2.2 #m are presented in Figs 186 a--d (the shift of the electrical zero level of the C250 has also been corrected). Agreement between theoretical and experimental curves is quite good. As an example of absorbing particles the response was measured also for Methylene Blue particles• In this case the refractive index varies
(a)
(b) 10
100 I
R 245 10
Z
/,...
•
OOP
. /
o
PSL
1,~.."
•
MB
.f
1.0
.""
C 208
4
]-7
/~
•
OOp
~'
o
PSL
//
n
# 4
-MB
..1
7
~
#// # i i-
~.0
0.1 i 1
001
.'i
o~ ;.
I
133 I ~.55
I592 -~ ..... ~50-001, J
0001
..... ISO-O01, ....... 196 - 0 661
I
0 0001
. . . .
,,,,i
O]
. . . . . . . .
i
~0
# i •
10
0.1
100
i0
- ......
~gs-0.6s,
10
100 O~ (ym)
Op (pro)
(c)
(d)
10
IO
C 250 •
I
J
00l
. . . . . . . .
. . . . . . . .
i
'7
. . . . . .
"~,
'
......
1
R218
1
:
o PSL • .B
i
.liIJ'7/"...,,. --
~
•
DOP
o
PSL
/'&' "
-i
~../i
,
10
,!i I 0.1 m
00~
!
. . . .
133
II
.....
165-001~
I
.......
196-
00l I
I0
I0
I00 Op UJm)
33
li
........... ~ 592
.......
I I I
0001 [ 01
,
J , ii
7
2.2.:
II
066i
0 001i 01
°'I
m
I
~ 9 6 - 0661
!
" 4 I i
,,•l
. . . . . . . .
10
Fig. 1861a-d). E x p e r i m e n t a l a n d theoretical responses o i lhe OPCs.
I
~0
. . . . .
IHI
lO0 DL~ (urn)
The Tenth Annual Conference of the Association for Aerosol Research
363
remarkably as a function of wavelength. Imaginary part is large a'. the effective wavelength range of C208 and R245 and small at the wavelength range used in the R218 and C250. Egan (1982) gives for m values 1.34-0.54i at 550 nm and 1.52~).016i at 820 nm. Because the m was not known in greater detail exact calculations could not be made. The general behavour of the theoretical curves, however, agrees well with these given values. As a conclusion it can thus be said that if the optical parameters of the counter are known the response can be predicted quite accurately with the aid of theoretical calculations. It can also be seen from the figures that even such values of absorption which are common in atmospheric aerosols change the response considerably.
REFERENCES Egan, W. G. (1982) Appl. Opt. 21° 1445. Cooke, D. D. and Kerker, M. (1975) Appl. Opt. 14, 734. M~ikynen. J.. Hakulinen, J., Kivist0, T. and Lehtimiiki, M. (1982) J. Aerosol Sci. 13, 529. Pinnick, R. G.. Rosen, J. M. and Hofmann, D. J. (1973) Appl. Opt. 12, 37. Wiscombe, W. (1979) NCA R Technical Note, NCA R/TN- 140 + STR.
A HIGH
RESOLUTION ELECTRICAL SPECTROMETER
MOBILITY (MAS)
AEROSOL
A. PLOMP, H. M. TEN BRINK, H. SPOELSTRA and J. F. VAN DE VATE Netherlands Energy Research Foundation, Petten, The Netherlands INTRODUCTION Present techniques used to measure the size of suboptical particles (d < 0.1/.tin) are based on the selection of aerosol according to mobility. The disadvantage o f t b e available instruments is their low size-resolution. The low resolution of the EAA (Electrical Aerosol Analyzer, TS13030) for instance is a consequence o f the low sensitivity o f t b e method to measure the concentration of the aerosol (viz. via the determination o f the charge on the particles). Recently Hoppel (1978) used a condensation nuclei counter to measure the concentration o f aerosol classified according to electrical mobility in a differential mobility chamber. Recently TSI introduced a continuous condensation nuclei counter of a novel design. According to the specifications (Liu and Pui, 1974) this instrument seemed to be well suited to be operated for the recording of the aerosol transmitted in a commercial Differential Mobility Analyzer (TSI 3071). It will be shown in the present presentation that the new combination constitutes a true aerosol spectrometer with high resolution for particles in the range o f 0.02-1/am.
MATERIALS
AND
METHODS
The new spectrometer is a combination of a commercial D M A (Differential-electrical-MobilityAnalyzer, TSI 3071) and a C C N C (Continuous Condensation Nucleus Counter, TSI 3020). A detailed description of the C C N C can be found in the recent literature(Liu and Pui, 1974).It might be best to summarize here those featuresof the instrument which are of importance for the present application. The C C N C is capable of detecting a concentration of as low as one particlein hundred c m 3 of air.Sampling of the aerosol in the condensation chamber, which is of the diffusion type, occurs in an uninterrupted continuous flow and the flow is almost insensitive to pressure drops of up to 60 cm H20. The performance of the C C N C was checked using a calibrated E S P / E M method (Van de Vate and Plomp, 1977) and a dilution method (Raes and Plomp, 1983). Aerosol for the calibration was obtained by nebulizing and subsequently drying o f solutions of uranine and NaCI in water; in this way a polydisperse aersol, characterized by lognormal distribution (dg = 0.06 #m, ag = 1.7) was obtained. A detailed description of a DMA is found in Hoppel (1978). Hence a short resum6 of the commercial apparatus will be given here. Basically the DMA consists of a concentrical, cylindrical condensator. An aerosol stream, imbedded in a concentrical sheath of air, is lead through this condensator. The charged fraction of the aerosol is deflected if an electrical field is applied. Particles acquire terminal velocities perpendicular to the main stream according to electrical mobility. At the narrow exit slit in the central electrode a well-defined mobility fraction of the positively charged aerosol is transmitted at a given value o f the electrical field. Thus aerosol particles can be selected by varying the electrical field. A reciprocal relation between applied voltage and the electrical mobility of the selected aerosol exists of the following form:
(1)
Zs= ~
where Z s is the electrical mobility, V is the voltage difference in the condensator, Q t and Qa are the flow rates o f the total flow and aerosol stream respectively. The proportionality factor ~ has a fixed value for the DMA (McMurry, 1977). In the present application Qt equals 3.31/min and Qa 0.3 l/min and thus the relation simplifies to: l
Z s = 0.132~.
(2)
Electrical mobility of particles can be translated to actual size via the following relation: ds
fl.n.C. Zo
(lb)