- Email: [email protected]
The growth of ambient aerosols in the conditions of the respiratory system
1. Aerosol SCI.. Vol 16, No 6, PP 521-527.
1985
WZI-8502/85 $3.00 +O.OO % 1985 Pergamon Press Ltd
Printed in Great Bntam
THE GROWTH
OF AMBIENT AEROSOLS IN THE CONDITIONS OF THE RESPIRATORY SYSTEM J. F. HICKS~~~ W. J. MEGAW
ppartment
of Physics, York University, 4700 Keele Street, North York, Ontario M3J IP3, Canada (Received 12 March 1985)
Abstract-The effect on ambient aerosols of exposure to the conditions of the respiratory system was determined by sampling simultaneously through two dichotomous samplers in parallel. In one of the samplers the aerosol was brought to 37°C and near 100% relative humidity before passing through the virtual impactor. The results show that, as a result of humidification, about 10-l 5 % by mass of the aerosol which would normally been collected in the fine (less than 2.5pm aerodynamic diameter) fraction of the sample grows sufficiently when humidified to be collected with the coarse fraction. It is suggested that the direct application to inhalation studies of dichotomous sampler results should be approached with some caution.
1. INTRODUCTION Dichotomous samplers are widely used to separate ambient aerosols into fine and coarse particulate fractions. They do this by rejecting particles of greater than 15 pm aerodynamic diameter and by making an inertial cut at an aerodynamic diameter of 2.5 jmr. It is considered that the smaller fraction will be preferentially deposited in the lower and the larger in the upper regions of the respiratory tract. This rather rough and ready approach to the estimation of possible hazards from inhaled aerosols has the virtue of simplicity, but overlooks the fact that the size cut is made in the temperature and humidity conditions of the atmosphere while the particles are deposited in the temperature and humidity conditions of the respiratory system. Inhaled particles, if they have some water soluble component, will, when exposed to the saturated air in the respiratory system, grow into droplets of larger size and their subsequent deposition behaviour will be governed by the aerodynamic diameter of the droplet. The situation is not helped by the fact (Table 1) that most experimental studies of the retention of aerosols in the respiratory system have been performed using insoluble aerosols, while, as will be seen, most of the ambient aerosol, even in industrial areas, is water soluble (Table 2). This work was performed with a view to determining the seriousness of this effect. Two identical dichotomous samplers were run in parallel sampling the ambient aerosol. In one of them the aerosol was sampled directly while in the other aerosol was brought to 37°C and near 100 % relative humidity before the size cut was made. The effect of aerosol growth could be estimated by comparison of the masses of the small and large fractions of the collected aerosol in the two samplers.
2. EXPERIMENTAL
2.1. Humid@cation
system
Absorbent artificial chamois was wrapped around a wire mesh cylinder 1 cm internal diameter and 1 m long. The chamois was then covered in plastic wrap to prevent water and air leakage through the walls of the column. The column was inserted into a 3 cm i.d. x 9Ocm-long stainless-steel tube. The open ends of the column were fitted to allow attachment to the dichotomous sampler between the virtual impactor and the inlet head. A 3 mm diameter hole was drilled through the outer shell to the chamois at the top of the column and a bulkhead fitting inserted to allow water to be added to saturate the chamois; the water was added by means of a syringe injection drive unit. Heating tape was wrapped around the humidifier tube to vapourize the water from the chamois and to warm the ambient air to 37°C. The power 521
522
J.
F. HICKS and
W. J.
MEGAW
Table 1. Test aerosols used in respiratory deposition studies Test aerosol
Reference Brown et al. (1950) Altshuler et al. (1967) Giacomelli-Maltoni et ai. (1972) Martens and Jacobi (1973) Heyder et 01. (1973) Rudolf et of. (1974) Lippmann (1977) Foord et al. (1980)
Solubility
China clay Triphenyl phosphate Carnauba wax Polystyrene latex di (2-ethylhexyl) sebacate di (2-ethylhexyl) sebacate Ferric oxide Polystyrene latex
Table 2. Solubihty of fine and coarse fractions of ambient aerosol
Filter number
Initial load (pg)
Weight loss
464
503 392 566 655
51 45 36 34 50
633 206 538 691 280
72 60 73 71 73
Coarse fractions 1681C 1689C 1691C 169x: 1697C Fine fractions 1690F 1694F 1696F 1698F 1704F Average weight loss. Coarse fraction Fine fraction
( 7,)
43 % (34-52 %). 70 % (60-73 %).
supplied to the heating tape was controlled externally by a variable transformer since the amount of heat required varied with the temperature of the incoming air. A similar column, but with a dry chamois and no heating tape, was fitted to the second dichotomous sampler so as to equalize any possible losses by impaction in the two tubes. After the humidified airstream had passed through the virtual impactor the air was dried by raising its temperature (and hence lowering its relative humidity) by means of a separately controlled heating tape in order to prevent condensation of water on the collection filters. Figure 1 shows the temperature and humidity profile of the air passing down the humidified column. Repeated measurements were taken by lowering wet and dry bulb telethermometers down the inner bore of the column. Care was taken to prevent wetting of the dry bulb. These measurements represent average values across the bore of the column and do not account for any variance in temperature and humidity through the cross-sectional area. The time of one second taken by the sampled air to pass down the column approximates to the time taken by inspired air to pass from the nose to the terminal bronchioles. Thus, the column effectively simulates the humidity and temperature conditions in the nasopharyngeal and tracheobronchial regions of the respiratory system, to which particulates are exposed during the inspiration stage. 2..2. Determination of soluble fraction of ambient aerosol In a preliminary series of experiments the filters from five runs of a dichotomous sampler were weighed and each filter was placed in a Buchner funnel attached to a vacuum. Three millilitres of deionized distilled water at 22°C were spread over the surface of the filter in 1 ml aliquots. The filters were then dried and reweighed. The results are given in Tables 2 and 3 for
523
Growth of ambient aerosols in the respiratory system AMBIENT
AIR
I (--
OUTSIDE
c
AIR
22
C
35%
RH
0.1
set
27°C
35%
RH
0.2
set
32°C
BS%
RH
0.3
set
3fC
50%
RH
0.4
SbC
37”
88%
RH
0.5
SBC
37’c
00%
RH
0.6
**c
3&C
93%
RH
0.7
set
3dC
95%
RH
0.6
set
35O c
95%
RH
0.0
set
3e
88%
RH
1.0
*ec
34’C
97%
RH
C
i
c
I
1
r=
VIR PARTIt
t
I
c
I
AL IMPACTOR F SIZE SEPARATOR
Fig. 1. Temperature and humidity profile of air in column.
the fine (less than 2.5 pm aerodynamic diameter) and the coarse (between 2.5 and 15 pm aerodynamic diameter). It is apparent that about 40 y0 by mass of the coarse fraction of the collected aerosol and about 70 y0 of the fine fraction is soluble in water and therefore capable of growth by condensation in the respiratory system. The solubility of the various elements present in the fine fraction is shown in Table 3. 2.3. Parallel operation of dry and humidified dichotomous samplers The samplers were placed on the roof of a downtown Toronto office building in an area exposed to pollution from vehicles and industry in addition to the natural aerosol. The samplers were well ventilated and close enough to be sampling the same aerosol without mutual interference. The exposures took place between October and December 1982. Some results were obtained during the pollution incident of 26-29 October when the Air Pollution Index exceeded 53 (the Ontario Air Pollution Index is calculated from the particulate and sulphur dioxide content of the air; values up to 32 are considered acceptable and at a value of 50 major sources of pollution are selectively shut down). It was determined by experience that adequate samples could be acquired after 28 hr of operation, although during heavy pollution episodes this period could be shortened to as little as 4 hr. Samples were taken during periods of both light and very heavy pollution. The samplers were checked visually
J. F. HICKS and W. J. MEGAW
524
Table 3. Solubility by element of fine fraction of ambient aerosol
Element
Mean percentage soluble (by weight)
Al Si
55 21 77 93 76 90 66 8 55 24 65 14 48 59 56 72 73 12 83 55 69
sp Cl K Ca Ti V Cr Mn Fe cu Zn As se Br % Ba Pb
every 2 hr during sampling and the flow rates, column temperature and humidity verified and corrected if necessary and the syringe system on the humidified column refilled with distilled water. Although the sampler required regular adjustment it maintained stable operating conditions within prescribed limits (95 + 3 % R.H. and 37 &4”C). As will be seen from theoretical considerations, variation of the conditions within these limits should not produce a noticeable change in the results. Four filters were obtained from each run, a fine and a coarse deposit (DF and DC) from the unhumidified, unheated sampler and corresponding filters (WF and WC) from the humidified heated sampler. 2.4. Gravimetric
analysis
Each of the four filters was weighed before and after sampling in air at 25°C and 42 + 2 % relative humidity. The filters were irradiated with a weak polonium source before weighing to reduce electrostatic charges. The balance used was an electromicrobalance (CAHN 50) which weighs consistently to + 2 pg. The sample weight was usually greater than 100 pg so that sensitivity was adequate to detect any significant displacement of sample from fine to coarse size ranges. 3. RESULTS
3.1. Preliminary
test experiment
The degree to which the deposition of particles in the modified samplers had been balanced was tested in a series of runs in which the test sampler was without humidification and the results compared with those from the control sampler. The results are given in Table 4 and it is apparent that the samplers agree within about 2 Y0in the majority of cases. These results are plotted in Figs 2, 3 and 4 as the ‘standard’ line. 3.2. Main experiment The test sampler was then run with the humidity unit operating (i.e. incoming air heated and humidified in test sampler but not in control sampler). Fifteen sets of samples were
525
Growth of ambient aerosols in the respiratory system Table 4. Comparison
of dry and wet (but unhumidikd)
columns
Wet column (unhumidified)
Dry column
Coarse
Fine
Total
Coarse
Fine
Total
421 255 264 186 211 255 85
533 332 389 210 283 306 124
960 587 653 396 494 561 209
439 256 261 188 206 261 83
562 324 393 214 279 311 124
1001 580 654 402 485 512 201
420’
380.
300.
240.
-EXPERIMENTAL ----STANDARD
180~
120Y
z
1.14x
- 1.1
CORRELATION
DRY COLUMN
- COARSE
COEFFICIENT
PARTICULATE
MASS
= 0.995
(ug/filter)
Fig. 2. Comparison of coarse mass loadings from dry and humid&xl columns.
,,/I-
320-1 280. 240. 200.
-EXPERIMENTAL 180.
----STANDARD
120.
Y=
0.072x
CORRELATION
DRY COLUMN
- FINE
PARTICULATE
+ 4.0 COEFFICIENT
MASS
(ug/filterI
Fig. 3. Comparison of fine mass loadings from dry and humidified columns.
= 0.994
526
J. F. HICKS and W. J. MEGAH. 750. z
700.
2
650. 800.
2
550.
/
,’ / _, / ,
2”
+e
_,, ’
,“” ___
EXPERIMENTAL
---STANDARD
w
200. Y
1.02x
=
-
4.7
CORRELATION
COEFFICIENT
500
DRY
Fig. 4. Comparison
COLUMN
- TOTAL
of total mass loadings
Table 5. Comparison
MASS
from dry and humidified
loadings
600
650
0.999
700
750
(ug/filterl
of dry and humidified
Sample
550
z
columns.
columns
(pg) Wet column (Heated and humidified)
Dry column
CoarSe
Fine
Total
Coarse
Fine
Total
351 141 80 158 148 110 95 102 75 154 143 112 128 208 124
347 108 123 187 193 173 163 63 108 85 220 260 146 138 221
698 249 203 345 341 283 258 165 183 239 363 372 274 346 345
406 159 98 185 158 117 110 106 84 166 172 133 143 227 143
306 97 105 160 180 164 145 60 98 76 196 227 126 133 198
712 256 203 345 338 281 264 166 182 242 368 360 269 360 341
obtained for gravimetric analysis and the results are listed in Table 5. All of them show that the WF (humidified fine) samples are lower in mass than the DF (control) samples and the WC (humidified coarse) samples greater in mass than the DC (control) samples. The results are plotted in Figs 2 to 4. A curve of the results from Table 4 (test sampler run unhumidified vs control sampler) is included for comparison. The curves show a significant shift as follows: (1)
WC samples are greater in mass than DC samples, WC = 1.14DC - 1.1.
(2)
WF samples are less in mass than DF samples, WF = 0.87 DF + 4.0.
(3)
The total masses in each experiment are very similar, WC+WF=DC+DF.
Growth of ambient aerosols in the respiratory system
527
From these results it is apparent that some small particles grow to greater than 2.5 pm aerodynamic diameter within the respiratory system and that between 10 and 15 y0 of the fine fraction of the ambient aerosol will do so. 4. DISCUSSION
Although the test and control samplers were geometrically similar, it is necessary to consider the effect of warm humid air in the test sampler on the sampler performance. The change in volume flow due to vapour addition varies with the initial humidity of the inlet air, but should never exceed 0.3 %. The expansion of air due to heating will affect the impactor performance. The change in cut point can be determined from Marple’s (1970) curves of impactor operating characteristics and it was found that, on an average sampling day, the cut point would be lowered from 2.5 to 2.42 pm. While this change is significant it is expected that the net effect on coarse/fine filter deposition would be small. The results indicate that due to the growth of the soluble fraction of the ambient aerosol when inhaled a shift occurs in particle size across the notional boundary of 2.5 pm aerodynamic diameter separating upper and lower respiratory retention. In addition to changing the region of retention the growth of droplets will probably increase overall retention. In addition postulated clearance mechanisms assume that the inhaled particles are insoluble and further work is obviously needed to determine whether they also apply to inhaled droplets. In the meantime air pollution toxicology results based on measurements with (dry) dichotomous samplers should be treated with some reserve. REFERENCES Altshuler, B., Palmes, E. D. and Nelson, N. (1967) Inhaled Particles and Vapours (Edited by Davies, C. N.), p. 323. Pergamon, Oxford. Brown, J. H., Cook, K. M., Ney, F. G. and Hatch, T. (1950) Am. J. Pub. Hlth 40, 450. Foord, N., Black, A. and Walsh, M. (1978) J. Aerosol Sci. 9, 343. Giacomelli-Maltoni, G., Meladri, D., Prodi, V. and Tarroni, G. (1972) Am. Ind. Hyg. Assoc. J. 603. Heyder, G. and Gebhart, G. (1980) J. Aerosol Sci. 11, 505. Lippman, M. (1977) Handbook of Physiology (Edited by Lee, D. H. K., Falk, H. L. and Murphy, S. D.), p. 213. American Physiological Society, Bethesda, Maryland. Marple, V. A. (1970) Ph.D. Thesis, University of Minnesota. Martens, A. and Jacobi, W. (1973) Aerosol in Physik, Me&in, and Technik (Edited by Bohlau, V.), p. 117, Gesellshaft fur Aerosoforschung, Bad Soden, F.R.G. Rudolf, G. and Heyder, J. (1974) Aerosol in Natunvissenchaft, Me&in and Technik (Edited by Bohlau, V.). Gesellschaft fiir Aerosolforschung, Bad Soden, F.R.G.
1985
WZI-8502/85 $3.00 +O.OO % 1985 Pergamon Press Ltd
Printed in Great Bntam
THE GROWTH
OF AMBIENT AEROSOLS IN THE CONDITIONS OF THE RESPIRATORY SYSTEM J. F. HICKS~~~ W. J. MEGAW
ppartment
of Physics, York University, 4700 Keele Street, North York, Ontario M3J IP3, Canada (Received 12 March 1985)
Abstract-The effect on ambient aerosols of exposure to the conditions of the respiratory system was determined by sampling simultaneously through two dichotomous samplers in parallel. In one of the samplers the aerosol was brought to 37°C and near 100% relative humidity before passing through the virtual impactor. The results show that, as a result of humidification, about 10-l 5 % by mass of the aerosol which would normally been collected in the fine (less than 2.5pm aerodynamic diameter) fraction of the sample grows sufficiently when humidified to be collected with the coarse fraction. It is suggested that the direct application to inhalation studies of dichotomous sampler results should be approached with some caution.
1. INTRODUCTION Dichotomous samplers are widely used to separate ambient aerosols into fine and coarse particulate fractions. They do this by rejecting particles of greater than 15 pm aerodynamic diameter and by making an inertial cut at an aerodynamic diameter of 2.5 jmr. It is considered that the smaller fraction will be preferentially deposited in the lower and the larger in the upper regions of the respiratory tract. This rather rough and ready approach to the estimation of possible hazards from inhaled aerosols has the virtue of simplicity, but overlooks the fact that the size cut is made in the temperature and humidity conditions of the atmosphere while the particles are deposited in the temperature and humidity conditions of the respiratory system. Inhaled particles, if they have some water soluble component, will, when exposed to the saturated air in the respiratory system, grow into droplets of larger size and their subsequent deposition behaviour will be governed by the aerodynamic diameter of the droplet. The situation is not helped by the fact (Table 1) that most experimental studies of the retention of aerosols in the respiratory system have been performed using insoluble aerosols, while, as will be seen, most of the ambient aerosol, even in industrial areas, is water soluble (Table 2). This work was performed with a view to determining the seriousness of this effect. Two identical dichotomous samplers were run in parallel sampling the ambient aerosol. In one of them the aerosol was sampled directly while in the other aerosol was brought to 37°C and near 100 % relative humidity before the size cut was made. The effect of aerosol growth could be estimated by comparison of the masses of the small and large fractions of the collected aerosol in the two samplers.
2. EXPERIMENTAL
2.1. Humid@cation
system
Absorbent artificial chamois was wrapped around a wire mesh cylinder 1 cm internal diameter and 1 m long. The chamois was then covered in plastic wrap to prevent water and air leakage through the walls of the column. The column was inserted into a 3 cm i.d. x 9Ocm-long stainless-steel tube. The open ends of the column were fitted to allow attachment to the dichotomous sampler between the virtual impactor and the inlet head. A 3 mm diameter hole was drilled through the outer shell to the chamois at the top of the column and a bulkhead fitting inserted to allow water to be added to saturate the chamois; the water was added by means of a syringe injection drive unit. Heating tape was wrapped around the humidifier tube to vapourize the water from the chamois and to warm the ambient air to 37°C. The power 521
522
J.
F. HICKS and
W. J.
MEGAW
Table 1. Test aerosols used in respiratory deposition studies Test aerosol
Reference Brown et al. (1950) Altshuler et al. (1967) Giacomelli-Maltoni et ai. (1972) Martens and Jacobi (1973) Heyder et 01. (1973) Rudolf et of. (1974) Lippmann (1977) Foord et al. (1980)
Solubility
China clay Triphenyl phosphate Carnauba wax Polystyrene latex di (2-ethylhexyl) sebacate di (2-ethylhexyl) sebacate Ferric oxide Polystyrene latex
Table 2. Solubihty of fine and coarse fractions of ambient aerosol
Filter number
Initial load (pg)
Weight loss
464
503 392 566 655
51 45 36 34 50
633 206 538 691 280
72 60 73 71 73
Coarse fractions 1681C 1689C 1691C 169x: 1697C Fine fractions 1690F 1694F 1696F 1698F 1704F Average weight loss. Coarse fraction Fine fraction
( 7,)
43 % (34-52 %). 70 % (60-73 %).
supplied to the heating tape was controlled externally by a variable transformer since the amount of heat required varied with the temperature of the incoming air. A similar column, but with a dry chamois and no heating tape, was fitted to the second dichotomous sampler so as to equalize any possible losses by impaction in the two tubes. After the humidified airstream had passed through the virtual impactor the air was dried by raising its temperature (and hence lowering its relative humidity) by means of a separately controlled heating tape in order to prevent condensation of water on the collection filters. Figure 1 shows the temperature and humidity profile of the air passing down the humidified column. Repeated measurements were taken by lowering wet and dry bulb telethermometers down the inner bore of the column. Care was taken to prevent wetting of the dry bulb. These measurements represent average values across the bore of the column and do not account for any variance in temperature and humidity through the cross-sectional area. The time of one second taken by the sampled air to pass down the column approximates to the time taken by inspired air to pass from the nose to the terminal bronchioles. Thus, the column effectively simulates the humidity and temperature conditions in the nasopharyngeal and tracheobronchial regions of the respiratory system, to which particulates are exposed during the inspiration stage. 2..2. Determination of soluble fraction of ambient aerosol In a preliminary series of experiments the filters from five runs of a dichotomous sampler were weighed and each filter was placed in a Buchner funnel attached to a vacuum. Three millilitres of deionized distilled water at 22°C were spread over the surface of the filter in 1 ml aliquots. The filters were then dried and reweighed. The results are given in Tables 2 and 3 for
523
Growth of ambient aerosols in the respiratory system AMBIENT
AIR
I (--
OUTSIDE
c
AIR
22
C
35%
RH
0.1
set
27°C
35%
RH
0.2
set
32°C
BS%
RH
0.3
set
3fC
50%
RH
0.4
SbC
37”
88%
RH
0.5
SBC
37’c
00%
RH
0.6
**c
3&C
93%
RH
0.7
set
3dC
95%
RH
0.6
set
35O c
95%
RH
0.0
set
3e
88%
RH
1.0
*ec
34’C
97%
RH
C
i
c
I
1
r=
VIR PARTIt
t
I
c
I
AL IMPACTOR F SIZE SEPARATOR
Fig. 1. Temperature and humidity profile of air in column.
the fine (less than 2.5 pm aerodynamic diameter) and the coarse (between 2.5 and 15 pm aerodynamic diameter). It is apparent that about 40 y0 by mass of the coarse fraction of the collected aerosol and about 70 y0 of the fine fraction is soluble in water and therefore capable of growth by condensation in the respiratory system. The solubility of the various elements present in the fine fraction is shown in Table 3. 2.3. Parallel operation of dry and humidified dichotomous samplers The samplers were placed on the roof of a downtown Toronto office building in an area exposed to pollution from vehicles and industry in addition to the natural aerosol. The samplers were well ventilated and close enough to be sampling the same aerosol without mutual interference. The exposures took place between October and December 1982. Some results were obtained during the pollution incident of 26-29 October when the Air Pollution Index exceeded 53 (the Ontario Air Pollution Index is calculated from the particulate and sulphur dioxide content of the air; values up to 32 are considered acceptable and at a value of 50 major sources of pollution are selectively shut down). It was determined by experience that adequate samples could be acquired after 28 hr of operation, although during heavy pollution episodes this period could be shortened to as little as 4 hr. Samples were taken during periods of both light and very heavy pollution. The samplers were checked visually
J. F. HICKS and W. J. MEGAW
524
Table 3. Solubility by element of fine fraction of ambient aerosol
Element
Mean percentage soluble (by weight)
Al Si
55 21 77 93 76 90 66 8 55 24 65 14 48 59 56 72 73 12 83 55 69
sp Cl K Ca Ti V Cr Mn Fe cu Zn As se Br % Ba Pb
every 2 hr during sampling and the flow rates, column temperature and humidity verified and corrected if necessary and the syringe system on the humidified column refilled with distilled water. Although the sampler required regular adjustment it maintained stable operating conditions within prescribed limits (95 + 3 % R.H. and 37 &4”C). As will be seen from theoretical considerations, variation of the conditions within these limits should not produce a noticeable change in the results. Four filters were obtained from each run, a fine and a coarse deposit (DF and DC) from the unhumidified, unheated sampler and corresponding filters (WF and WC) from the humidified heated sampler. 2.4. Gravimetric
analysis
Each of the four filters was weighed before and after sampling in air at 25°C and 42 + 2 % relative humidity. The filters were irradiated with a weak polonium source before weighing to reduce electrostatic charges. The balance used was an electromicrobalance (CAHN 50) which weighs consistently to + 2 pg. The sample weight was usually greater than 100 pg so that sensitivity was adequate to detect any significant displacement of sample from fine to coarse size ranges. 3. RESULTS
3.1. Preliminary
test experiment
The degree to which the deposition of particles in the modified samplers had been balanced was tested in a series of runs in which the test sampler was without humidification and the results compared with those from the control sampler. The results are given in Table 4 and it is apparent that the samplers agree within about 2 Y0in the majority of cases. These results are plotted in Figs 2, 3 and 4 as the ‘standard’ line. 3.2. Main experiment The test sampler was then run with the humidity unit operating (i.e. incoming air heated and humidified in test sampler but not in control sampler). Fifteen sets of samples were
525
Growth of ambient aerosols in the respiratory system Table 4. Comparison
of dry and wet (but unhumidikd)
columns
Wet column (unhumidified)
Dry column
Coarse
Fine
Total
Coarse
Fine
Total
421 255 264 186 211 255 85
533 332 389 210 283 306 124
960 587 653 396 494 561 209
439 256 261 188 206 261 83
562 324 393 214 279 311 124
1001 580 654 402 485 512 201
420’
380.
300.
240.
-EXPERIMENTAL ----STANDARD
180~
120Y
z
1.14x
- 1.1
CORRELATION
DRY COLUMN
- COARSE
COEFFICIENT
PARTICULATE
MASS
= 0.995
(ug/filter)
Fig. 2. Comparison of coarse mass loadings from dry and humid&xl columns.
,,/I-
320-1 280. 240. 200.
-EXPERIMENTAL 180.
----STANDARD
120.
Y=
0.072x
CORRELATION
DRY COLUMN
- FINE
PARTICULATE
+ 4.0 COEFFICIENT
MASS
(ug/filterI
Fig. 3. Comparison of fine mass loadings from dry and humidified columns.
= 0.994
526
J. F. HICKS and W. J. MEGAH. 750. z
700.
2
650. 800.
2
550.
/
,’ / _, / ,
2”
+e
_,, ’
,“” ___
EXPERIMENTAL
---STANDARD
w
200. Y
1.02x
=
-
4.7
CORRELATION
COEFFICIENT
500
DRY
Fig. 4. Comparison
COLUMN
- TOTAL
of total mass loadings
Table 5. Comparison
MASS
from dry and humidified
loadings
600
650
0.999
700
750
(ug/filterl
of dry and humidified
Sample
550
z
columns.
columns
(pg) Wet column (Heated and humidified)
Dry column
CoarSe
Fine
Total
Coarse
Fine
Total
351 141 80 158 148 110 95 102 75 154 143 112 128 208 124
347 108 123 187 193 173 163 63 108 85 220 260 146 138 221
698 249 203 345 341 283 258 165 183 239 363 372 274 346 345
406 159 98 185 158 117 110 106 84 166 172 133 143 227 143
306 97 105 160 180 164 145 60 98 76 196 227 126 133 198
712 256 203 345 338 281 264 166 182 242 368 360 269 360 341
obtained for gravimetric analysis and the results are listed in Table 5. All of them show that the WF (humidified fine) samples are lower in mass than the DF (control) samples and the WC (humidified coarse) samples greater in mass than the DC (control) samples. The results are plotted in Figs 2 to 4. A curve of the results from Table 4 (test sampler run unhumidified vs control sampler) is included for comparison. The curves show a significant shift as follows: (1)
WC samples are greater in mass than DC samples, WC = 1.14DC - 1.1.
(2)
WF samples are less in mass than DF samples, WF = 0.87 DF + 4.0.
(3)
The total masses in each experiment are very similar, WC+WF=DC+DF.
Growth of ambient aerosols in the respiratory system
527
From these results it is apparent that some small particles grow to greater than 2.5 pm aerodynamic diameter within the respiratory system and that between 10 and 15 y0 of the fine fraction of the ambient aerosol will do so. 4. DISCUSSION
Although the test and control samplers were geometrically similar, it is necessary to consider the effect of warm humid air in the test sampler on the sampler performance. The change in volume flow due to vapour addition varies with the initial humidity of the inlet air, but should never exceed 0.3 %. The expansion of air due to heating will affect the impactor performance. The change in cut point can be determined from Marple’s (1970) curves of impactor operating characteristics and it was found that, on an average sampling day, the cut point would be lowered from 2.5 to 2.42 pm. While this change is significant it is expected that the net effect on coarse/fine filter deposition would be small. The results indicate that due to the growth of the soluble fraction of the ambient aerosol when inhaled a shift occurs in particle size across the notional boundary of 2.5 pm aerodynamic diameter separating upper and lower respiratory retention. In addition to changing the region of retention the growth of droplets will probably increase overall retention. In addition postulated clearance mechanisms assume that the inhaled particles are insoluble and further work is obviously needed to determine whether they also apply to inhaled droplets. In the meantime air pollution toxicology results based on measurements with (dry) dichotomous samplers should be treated with some reserve. REFERENCES Altshuler, B., Palmes, E. D. and Nelson, N. (1967) Inhaled Particles and Vapours (Edited by Davies, C. N.), p. 323. Pergamon, Oxford. Brown, J. H., Cook, K. M., Ney, F. G. and Hatch, T. (1950) Am. J. Pub. Hlth 40, 450. Foord, N., Black, A. and Walsh, M. (1978) J. Aerosol Sci. 9, 343. Giacomelli-Maltoni, G., Meladri, D., Prodi, V. and Tarroni, G. (1972) Am. Ind. Hyg. Assoc. J. 603. Heyder, G. and Gebhart, G. (1980) J. Aerosol Sci. 11, 505. Lippman, M. (1977) Handbook of Physiology (Edited by Lee, D. H. K., Falk, H. L. and Murphy, S. D.), p. 213. American Physiological Society, Bethesda, Maryland. Marple, V. A. (1970) Ph.D. Thesis, University of Minnesota. Martens, A. and Jacobi, W. (1973) Aerosol in Physik, Me&in, and Technik (Edited by Bohlau, V.), p. 117, Gesellshaft fur Aerosoforschung, Bad Soden, F.R.G. Rudolf, G. and Heyder, J. (1974) Aerosol in Natunvissenchaft, Me&in and Technik (Edited by Bohlau, V.). Gesellschaft fiir Aerosolforschung, Bad Soden, F.R.G.