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Experimental measurements of aerosol concentrations in offices
Environment International, Vol. 8, pp. 223-227, 1982
0160-4120/82/070223-05503.00/0 Copyright © 1982 Pergamon Press Ltd.
Printed in the USA. All rights reserved.
EXPERIMENTAL MEASUREMENTS OF AEROSOL CONCENTRATIONS IN OFFICES F. R. Quant, P. A. Nelson, and G. J. Sem TSI Incorporated, 500 Cardigan Rd., P.O. Box 43394, St. Paul, MN 55164, USA
A new automated version of the piezoelectric microbalance measures the mass concentration of airborne particles smaller than a preselected aerodynamic cutoff diameter. It is designed for near-real-time, unattended, round-the-clock measurements of nearly any aerosol environment inhabited by. humans. The instrument uses an electrostatic precipitator to deposit particles with greater than 95% efficiency onto a piezoelectric quartz crystal sensor which is able to detect a deposit of 0.005/~g. The precipitator and sensor are nearly identical to those in the portable instrument reported previously. Measurements comparing within + 15% with gravimetrically measured filter samples are documented for a wide variety of aerosols in the 50 #g/m 3 to 5.5 mg/m3 range. The instrument measures particles from 10/zm down to 0.01 tim in diameter, including submicron combustion smokes and metallic fumes. The piezoelectric microbalance technique senses the mass concentration of the aerosol, rather than light scattering properties as is done by photometers and nephelometers. The piezobalance, with 1 L/rain sample flow, is more sensitive than any other mass-sensing instrument, making it especially suited for low concentration indoor measurements, even below 50 ~tg/m3. An automatic piezobalance recently measured respirable aerosol mass concentrations in several offices. Each measurement was the average concentration during a 30-min period. The 24-h/day measurements continued for several days. Especially interesting is the diurnal pattern, both for offices with and without smokers. The effect of a single nearby smoker was clearly illustrated when the smoker was absent one day in the middle of a week. Normal daytime peak concentrations in that office reached 80-110 #g/m 3 with a smoker present, but only 50-60 #g/m 3 when the smoker was absent. Curious smokers who briefly stopped by to see the instrument caused single half-hour averages to triple, to values as high as 294 #g/m3 in one office.
Introduction The piezoelectric m i c r o b a l a n c e t e c h n i q u e has b e e n used for m a n y years in the m e a s u r e m e n t o f i n d u s t r i a l respirable aerosol mass c o n c e n t r a t i o n (Sem et al., 1975, 1977) a n d m o r e recently in the m e a s u r e m e n t o f o u t d o o r respirable c o n c e n t r a t i o n s ( T s u r u b a y a s h i et al., 1980, in pre~s). This p a p e r describes m e a s u r e m e n t s m a d e in ind o o r offices u s i n g a n e w m i c r o c o m p u t e r - c o n t r o l l e d piezoelectric i n s t r u m e n t c a p a b l e o f m e a s u r i n g respirable smokes, dusts, fumes, a n d other a i r b o r n e particles in the 0 . 0 1 - 1 0 ttm range.
Equipment T h e new i n s t r u m e n t utilizes the v i b r a t i n g q u a r t z crystal m i c r o b a l a n c e t e c h n i q u e . T h e aerosol is first precut by a cyclone (Sere a n d Q u a n t , in press) or a n impactor (Sem et al., 1977) to r e m o v e particles larger t h a n 3.5 /~m a e r o d y n a m i c diameter. T h e smaller, respirable particles are then electrostatically precipitated with greater
t h a n 95°7o collection efficiency o n t o the piezoelectric q u a r t z crystal sensor (Sem a n d T s u r u b a y a s h i , 1975). T h e mass o f the particles decreases the crystal's n a t u r a l v i b r a t i o n a l f r e q u e n c y by 180 H z o f f r e q u e n c y for every #g o f precipitated mass. A b u i l t - i n m i c r o c o m p u t e r calculates the respirable mass c o n c e n t r a t i o n , based o n the f r e q u e n c y shift, sample time, sensitivity, a n d the c o n s t a n t 1 - L / m i n sample flow rate. A t the e n d o f a sample, the processor calculates a n d prints the time, mass c o n c e n t r a t i o n , a n d mass c o n c e n t r a t i o n which has been averaged over a selected n u m b e r o f samples (Sem a n d Q u a n t , in press). T h e m i c r o c o m p u t e r t h e n initiates a n a u t o m a t i c cycle to clean the piezoelectric sensor. The m i c r o c o m p u t e r gives the o p e r a t o r m u c h flexibility for setting u p the length o f sample time, f r e q u e n c y o f s a m p l i n g , time o f day, date, p r i n t rate, a n d c o n c e n t r a t i o n display. O n c e set up, the i n s t r u m e n t samples cont i n u o u s l y a n d u n a t t e n d e d for u p to 2 weeks while measuring 3 0 - m i n consecutive samples. T h e older p o r t a b l e piezoelectric m i c r o b a l a n c e has a precutter, precipitator, a n d sensor which are essentially 223
224
identical to those on the automatic instrument. Sem et al. (1977) and Sere and Quant (in press) reported extensive comparisons o f portable piezoelectric microbalance measurements with gravimetrically measured filter samples for a variety of respirable aerosols. Included were indoor aerosols, tobacco smoke, welding fumes, oil mist, cotton, copper and asbestos mill dusts, powdered metal and walnut shell abrasive dusts, die casting aerosols, and combinations o f several aerosols. Concentrations varied from 50 # g / m 3 to 5.5 m g / m 3. The piezoelectric microbalances measured within ± 15% of the average o f two filter measurements for nearly every measurement. Sem and Tsurubayashi (1977) described their sampling system and procedures in detail and emphasized the care needed to obtain two valid filter samples which agree with each other. Tsurubayashi and Kano (1980) and Tsurubayashi et al. (in press) report results of outdoor respirable aerosol sampling with their automatic piezobalance which has a precipitator and sensor identical to those in the instrument reported here. They reported good agreement between the piezoelectric microbalances and the Japanese standard low-volume filter sampler with gravimetric analysis. Fairchild et al. (1980) reported a large set of experimental comparisons o f portable piezoelectric microbalances and other fast response respirable aerosol mass monitors with gravimetric measurements of three different filter samples. They had some difficulty with comparisons between the three filter samples. When the three filters did agree with each other, the two piezoelectric microbalances generally agreed well with the filters for respirable aerosols. They found considerably better agreement between the two piezoelectric instruments than between the three filter samples on the majority of the tests with respirable aerosols. Sem and Quant (in press) reported that the piezoelectric microbalance sometimes exhibits a positive zero offset when measuring some indoor aerosols; this is probably caused by the gas-to-particle conversion of a trace gaseous component while the aerosol passes through the electrostatic precipitator. The value of the zero offset may be measured by connecting a high-efficiency particle filter to the inlet of the precipitator. In our experience, the zero offset is usually in the 0-30 #g/m 3 range and is usually very stable in any single location. The zero offset has not been noticed in outdoor atmospheres and is not present in many indoor environments. The zero offset usually disappears when an activated charcoal filter is connected to the precipitator inlet. The measured value of the zero offset should be subtracted from the normal concentration measurements, especially when measuring concentrations below several hundred /~g/m 3. All data in this article has had a zero offset of 15 #g/m 3 subtracted from the concentration values.
F.R. Quant, P. A. Nelson, and G. J. Sem
Methods We measured respirable aerosol mass concentration using the new instrument in three offices chosen as a reasonable cross section of smoking and nonsmoking areas. Two offices were 130 m 2 and the other was 280 m 2. All three were divided into cubicles by half-wall dividers. Each office contained between 15 and 18 employees. Due to the flexible working hours at the plant, employees arrived between 6:30 and 8:30 a.m. and left between 3:00 and 5:00 p.m. Lunch break was any 30min period between 11:30 a.m. and 1:00 p.m. Samples were taken over 30-min periods. Continuous 1-week measurements were made in each office. The accounting office contained three smokers, none of whom were closer than 3 m to the instrument. Two instruments operated side-by-side for the first half of the week to determine the correlation between them. All "week-long" measurements were made by the same sensor. The R & D office had the larger floor area. Only about one-half of the room, the outer perimeter, used cubicle office spaces. The one smoker in the room was located at the opposite side of the room, about 10 m away from the instrument. This office area also had the
T
Fig. 1. Two automatic piezoelectric microbalances in an office with the control and printer module (top), sensor module (middle), and cleaning reservoir (bottom). The sample inlet is at the top of the white stack.
Measurement of aerosol concentrations
225
200
150
t
. . . . . .
100
50
-=
JJJJ
0
JJJJJJJJ
Z
300 .< nl-Z _ ~ 2 5 0
Z
o
o (n 200 u~ <
:S 150-
-[
I
100- - - i
50-
0 0000
1
12O0 22 JUNE MON
/
0000
1200 23 JUNE
0000
TUE
1200 24 JUNE
0000
WED
1200 25 JUNE
THU
0000
1200 26 JUNE
0000
FRI
Fig. 2. Aerosol mass concentration in accounting office taken by two side-by-side instruments. The office contained 3 smokers; none were closer than 3 m to the instruments except during the peak measurements. One'smoker worked late the night of 23 June.
least ventilation with four pairs of inlet and outlet vents, as opposed to six pairs of vents for each of the other office areas. In the engineering office, the instrument was located in a cubicle next to one occupied by a smoker. A second smoker was located at the far end of the room. Figure 1 shows two instruments as they were taking measurements in one of the offices. Results
Figure 2 shows the data from the accounting office. A diurnal cycle is evident as respirable concentrations increased rapidly after 7:00 a.m. each morning and gradually decreased each afternoon after 3:30 p.m. Correlation between the two sensors was excellent. Several high respirable concentrations of over 100 #g/m 3 were observed during the week caused by smoking employees who were looking at the instrument out of curiosity. The concentrations measured during these periods varied significantly between the two instruments, probably because the instruments had separate aerosol inlets
located about 0.7 m apart. The concentration dropped each day around noon corresponding to the employee lunch break. Evening and weekend respirable concentrations dropped to 5-15 #g/m 3 while daytime levels were in the 35-65 #g/m 3 range. Figure 3 shows the data gathered from the R & D office. Measured concentrations were similar to those in the accounting office, with evening and weekend between 15 and 20 #g/m 3 and daytime readings between 35 and 55 /~g/m 3. Figure 4 shows data from the engineering office. The respirable concentrations were much higher during the day with several episodes over 100 #g/m 3. Only four cycles are evident because Friday was a holiday. The absence of the heavy smoker on Wednesday reduced the concentration considerably on that day. Comparisons
We calculated the average measured respirable concentration for daytime periods between 7:00 a.m. and 5:00 p.m. These averages are tabulated in Table 1.
226
F.R. Quant, P. A. Nelson, and G. J. Sem
3o0 fill; t 150~ !
1200
OO00
1200
00OO
1200
0000
1200
O000
1200
0000
1200
6 JULY
7 JULY
8 JULY
9 JULY
10 JULY
11 JULY
MON
TUE
WED
THU
FRI
SAT
Fig. 3. Aerosol massconcentrationin R & D office. No smokers were neartheinstrumentexcepton 9July when a curioussmokerbrieflystopped by.
T h e m e a s u r e d a v e r a g e s f o u n d in the a c c o u n t i n g a n d R & D offices a r e very similar. T h e large p e a k s t h a t occ u r r e d in the a c c o u n t i n g o f f i c e were offset b y the p o o r e r v e n t i l a t i o n in the R & D a r e a . T h e engineering office exh i b i t e d a h i g h e r a v e r a g e c o n c e n t r a t i o n t h a n either o f the o t h e r areas. T h e d a y t i m e a v e r a g e in the engineering office w h e n the s m o k e r was a b s e n t was c o m p a r a b l e to c o n c e n t r a t i o n s in b o t h o f the o t h e r offices. T h e engineering o f f i c e also e x h i b i t e d the largest v a r i a t i o n in con-
secutive c o n c e n t r a t i o n m e a s u r e m e n t s d u e to the close proximity of a smoker.
Conclusions
The diurnal respirable aerosol mass concentration p a t t e r n s in offices can easily be m e a s u r e d with the a u t o m a t i c v i b r a t i n g piezoelectric q u a r t z crystal m i c r o b a l a n c e t e c h n i q u e . T h e increases a n d decreases in m a s s
300 i 250-
~
200
I'-" Z 150 UJ Z O O lOO (n u) =f
50
1200 0 2 9 JUNE
MON
0000
1200 3 0 JUNE
TUE
0000
1200 1 JULY
WED
O000
1200 2 JULY
THU
0OO0
1200 3 JULY
FRI
0OO0
1200 4 JULY
SAT
Fig. 4. Aerosol mass concentration in engineering office. A smoker's office was nearby. The smoker was absent on 1 July, 3 July was a holiday, and 4 July was a nonworking Saturday.
Measurement of aerosol concentrations
227
Table 1. Average measured respirable concentrations for three offices during daytime periods. Day
Accounting
R&D
Engineering
1
39 46 39 54 46 45 #g/m ~
37 50 49 46 42 45 #g/m 3
77 89 42 62 -67.5 ~g/m 3
2 3 4 5 Average
concentration are often readily identifiable. The causes of high concentrations are also identifiable by documenting the operations pertinent to the measurement, i.e., a smoker being present during a measurement period. This instrument will undoubtedly be used as a powerful tool in the measurement and documentation of respirable aerosol mass concentrations in offices, homes, work places, and other indoor environments.
References Fairchild, C. I., Tillery, M. I., and Ettinger, H. J. (1980) An evaluation of fast response aerosol mass monitors. Report No. LA-8220, Los Alamos Scientific Laboratory, Los Alamos, NM. Sem. G. J. and Quant, F. R. (in press) An automatic piezobalance respirable aerosol mass monitor for unattended real-time measurements, in Aerosols in the Mining and Industrial Work Environment. Vol. II1: Instrumentation, V. A. Marple and B. Y. H. Liu, eds. Ann Arbor Science, Ann Arbor, MI. Sem, G. J. and Tsurubayashi, K. (1975) A new mass sensor for respirable dust measurement, Am. Ind. Hyg. Assoc. J. 36, 791800. Sem, G. J., Tsurubayashi, K., and Homma, K. (1977) Performance of the piezoelectric microbalance respirable aerosol sensor, Am. Ind. Hyg. Assoc. J. 38, 580-588. Tsurubayashi, K. and Kano, H. (1980) Field testing of automatic piezoelectric microbalances for outdoor aerosol mass concentration measurements, EPA-600/9-80-004, Proceedings: Advances in Particle Sampling and Measurement, W. B. Smith, ed. pp. 217-241. Daytona Beach, FL, October 1979. Tsurubayashi, K., Kano, H., and Hayakawa, I. (in press) Mass concentration measurement by piezobalance dust meters, in Aerosols in the Mining and Industrial Work Environment. Vol. III: Instrumentation, V. A. Marple and B. Y. H. Liu, eds. Ann Arbor Science, Ann Arbor, MI.
0160-4120/82/070223-05503.00/0 Copyright © 1982 Pergamon Press Ltd.
Printed in the USA. All rights reserved.
EXPERIMENTAL MEASUREMENTS OF AEROSOL CONCENTRATIONS IN OFFICES F. R. Quant, P. A. Nelson, and G. J. Sem TSI Incorporated, 500 Cardigan Rd., P.O. Box 43394, St. Paul, MN 55164, USA
A new automated version of the piezoelectric microbalance measures the mass concentration of airborne particles smaller than a preselected aerodynamic cutoff diameter. It is designed for near-real-time, unattended, round-the-clock measurements of nearly any aerosol environment inhabited by. humans. The instrument uses an electrostatic precipitator to deposit particles with greater than 95% efficiency onto a piezoelectric quartz crystal sensor which is able to detect a deposit of 0.005/~g. The precipitator and sensor are nearly identical to those in the portable instrument reported previously. Measurements comparing within + 15% with gravimetrically measured filter samples are documented for a wide variety of aerosols in the 50 #g/m 3 to 5.5 mg/m3 range. The instrument measures particles from 10/zm down to 0.01 tim in diameter, including submicron combustion smokes and metallic fumes. The piezoelectric microbalance technique senses the mass concentration of the aerosol, rather than light scattering properties as is done by photometers and nephelometers. The piezobalance, with 1 L/rain sample flow, is more sensitive than any other mass-sensing instrument, making it especially suited for low concentration indoor measurements, even below 50 ~tg/m3. An automatic piezobalance recently measured respirable aerosol mass concentrations in several offices. Each measurement was the average concentration during a 30-min period. The 24-h/day measurements continued for several days. Especially interesting is the diurnal pattern, both for offices with and without smokers. The effect of a single nearby smoker was clearly illustrated when the smoker was absent one day in the middle of a week. Normal daytime peak concentrations in that office reached 80-110 #g/m 3 with a smoker present, but only 50-60 #g/m 3 when the smoker was absent. Curious smokers who briefly stopped by to see the instrument caused single half-hour averages to triple, to values as high as 294 #g/m3 in one office.
Introduction The piezoelectric m i c r o b a l a n c e t e c h n i q u e has b e e n used for m a n y years in the m e a s u r e m e n t o f i n d u s t r i a l respirable aerosol mass c o n c e n t r a t i o n (Sem et al., 1975, 1977) a n d m o r e recently in the m e a s u r e m e n t o f o u t d o o r respirable c o n c e n t r a t i o n s ( T s u r u b a y a s h i et al., 1980, in pre~s). This p a p e r describes m e a s u r e m e n t s m a d e in ind o o r offices u s i n g a n e w m i c r o c o m p u t e r - c o n t r o l l e d piezoelectric i n s t r u m e n t c a p a b l e o f m e a s u r i n g respirable smokes, dusts, fumes, a n d other a i r b o r n e particles in the 0 . 0 1 - 1 0 ttm range.
Equipment T h e new i n s t r u m e n t utilizes the v i b r a t i n g q u a r t z crystal m i c r o b a l a n c e t e c h n i q u e . T h e aerosol is first precut by a cyclone (Sere a n d Q u a n t , in press) or a n impactor (Sem et al., 1977) to r e m o v e particles larger t h a n 3.5 /~m a e r o d y n a m i c diameter. T h e smaller, respirable particles are then electrostatically precipitated with greater
t h a n 95°7o collection efficiency o n t o the piezoelectric q u a r t z crystal sensor (Sem a n d T s u r u b a y a s h i , 1975). T h e mass o f the particles decreases the crystal's n a t u r a l v i b r a t i o n a l f r e q u e n c y by 180 H z o f f r e q u e n c y for every #g o f precipitated mass. A b u i l t - i n m i c r o c o m p u t e r calculates the respirable mass c o n c e n t r a t i o n , based o n the f r e q u e n c y shift, sample time, sensitivity, a n d the c o n s t a n t 1 - L / m i n sample flow rate. A t the e n d o f a sample, the processor calculates a n d prints the time, mass c o n c e n t r a t i o n , a n d mass c o n c e n t r a t i o n which has been averaged over a selected n u m b e r o f samples (Sem a n d Q u a n t , in press). T h e m i c r o c o m p u t e r t h e n initiates a n a u t o m a t i c cycle to clean the piezoelectric sensor. The m i c r o c o m p u t e r gives the o p e r a t o r m u c h flexibility for setting u p the length o f sample time, f r e q u e n c y o f s a m p l i n g , time o f day, date, p r i n t rate, a n d c o n c e n t r a t i o n display. O n c e set up, the i n s t r u m e n t samples cont i n u o u s l y a n d u n a t t e n d e d for u p to 2 weeks while measuring 3 0 - m i n consecutive samples. T h e older p o r t a b l e piezoelectric m i c r o b a l a n c e has a precutter, precipitator, a n d sensor which are essentially 223
224
identical to those on the automatic instrument. Sem et al. (1977) and Sere and Quant (in press) reported extensive comparisons o f portable piezoelectric microbalance measurements with gravimetrically measured filter samples for a variety of respirable aerosols. Included were indoor aerosols, tobacco smoke, welding fumes, oil mist, cotton, copper and asbestos mill dusts, powdered metal and walnut shell abrasive dusts, die casting aerosols, and combinations o f several aerosols. Concentrations varied from 50 # g / m 3 to 5.5 m g / m 3. The piezoelectric microbalances measured within ± 15% of the average o f two filter measurements for nearly every measurement. Sem and Tsurubayashi (1977) described their sampling system and procedures in detail and emphasized the care needed to obtain two valid filter samples which agree with each other. Tsurubayashi and Kano (1980) and Tsurubayashi et al. (in press) report results of outdoor respirable aerosol sampling with their automatic piezobalance which has a precipitator and sensor identical to those in the instrument reported here. They reported good agreement between the piezoelectric microbalances and the Japanese standard low-volume filter sampler with gravimetric analysis. Fairchild et al. (1980) reported a large set of experimental comparisons o f portable piezoelectric microbalances and other fast response respirable aerosol mass monitors with gravimetric measurements of three different filter samples. They had some difficulty with comparisons between the three filter samples. When the three filters did agree with each other, the two piezoelectric microbalances generally agreed well with the filters for respirable aerosols. They found considerably better agreement between the two piezoelectric instruments than between the three filter samples on the majority of the tests with respirable aerosols. Sem and Quant (in press) reported that the piezoelectric microbalance sometimes exhibits a positive zero offset when measuring some indoor aerosols; this is probably caused by the gas-to-particle conversion of a trace gaseous component while the aerosol passes through the electrostatic precipitator. The value of the zero offset may be measured by connecting a high-efficiency particle filter to the inlet of the precipitator. In our experience, the zero offset is usually in the 0-30 #g/m 3 range and is usually very stable in any single location. The zero offset has not been noticed in outdoor atmospheres and is not present in many indoor environments. The zero offset usually disappears when an activated charcoal filter is connected to the precipitator inlet. The measured value of the zero offset should be subtracted from the normal concentration measurements, especially when measuring concentrations below several hundred /~g/m 3. All data in this article has had a zero offset of 15 #g/m 3 subtracted from the concentration values.
F.R. Quant, P. A. Nelson, and G. J. Sem
Methods We measured respirable aerosol mass concentration using the new instrument in three offices chosen as a reasonable cross section of smoking and nonsmoking areas. Two offices were 130 m 2 and the other was 280 m 2. All three were divided into cubicles by half-wall dividers. Each office contained between 15 and 18 employees. Due to the flexible working hours at the plant, employees arrived between 6:30 and 8:30 a.m. and left between 3:00 and 5:00 p.m. Lunch break was any 30min period between 11:30 a.m. and 1:00 p.m. Samples were taken over 30-min periods. Continuous 1-week measurements were made in each office. The accounting office contained three smokers, none of whom were closer than 3 m to the instrument. Two instruments operated side-by-side for the first half of the week to determine the correlation between them. All "week-long" measurements were made by the same sensor. The R & D office had the larger floor area. Only about one-half of the room, the outer perimeter, used cubicle office spaces. The one smoker in the room was located at the opposite side of the room, about 10 m away from the instrument. This office area also had the
T
Fig. 1. Two automatic piezoelectric microbalances in an office with the control and printer module (top), sensor module (middle), and cleaning reservoir (bottom). The sample inlet is at the top of the white stack.
Measurement of aerosol concentrations
225
200
150
t
. . . . . .
100
50
-=
JJJJ
0
JJJJJJJJ
Z
300 .< nl-Z _ ~ 2 5 0
Z
o
o (n 200 u~ <
:S 150-
-[
I
100- - - i
50-
0 0000
1
12O0 22 JUNE MON
/
0000
1200 23 JUNE
0000
TUE
1200 24 JUNE
0000
WED
1200 25 JUNE
THU
0000
1200 26 JUNE
0000
FRI
Fig. 2. Aerosol mass concentration in accounting office taken by two side-by-side instruments. The office contained 3 smokers; none were closer than 3 m to the instruments except during the peak measurements. One'smoker worked late the night of 23 June.
least ventilation with four pairs of inlet and outlet vents, as opposed to six pairs of vents for each of the other office areas. In the engineering office, the instrument was located in a cubicle next to one occupied by a smoker. A second smoker was located at the far end of the room. Figure 1 shows two instruments as they were taking measurements in one of the offices. Results
Figure 2 shows the data from the accounting office. A diurnal cycle is evident as respirable concentrations increased rapidly after 7:00 a.m. each morning and gradually decreased each afternoon after 3:30 p.m. Correlation between the two sensors was excellent. Several high respirable concentrations of over 100 #g/m 3 were observed during the week caused by smoking employees who were looking at the instrument out of curiosity. The concentrations measured during these periods varied significantly between the two instruments, probably because the instruments had separate aerosol inlets
located about 0.7 m apart. The concentration dropped each day around noon corresponding to the employee lunch break. Evening and weekend respirable concentrations dropped to 5-15 #g/m 3 while daytime levels were in the 35-65 #g/m 3 range. Figure 3 shows the data gathered from the R & D office. Measured concentrations were similar to those in the accounting office, with evening and weekend between 15 and 20 #g/m 3 and daytime readings between 35 and 55 /~g/m 3. Figure 4 shows data from the engineering office. The respirable concentrations were much higher during the day with several episodes over 100 #g/m 3. Only four cycles are evident because Friday was a holiday. The absence of the heavy smoker on Wednesday reduced the concentration considerably on that day. Comparisons
We calculated the average measured respirable concentration for daytime periods between 7:00 a.m. and 5:00 p.m. These averages are tabulated in Table 1.
226
F.R. Quant, P. A. Nelson, and G. J. Sem
3o0 fill; t 150~ !
1200
OO00
1200
00OO
1200
0000
1200
O000
1200
0000
1200
6 JULY
7 JULY
8 JULY
9 JULY
10 JULY
11 JULY
MON
TUE
WED
THU
FRI
SAT
Fig. 3. Aerosol massconcentrationin R & D office. No smokers were neartheinstrumentexcepton 9July when a curioussmokerbrieflystopped by.
T h e m e a s u r e d a v e r a g e s f o u n d in the a c c o u n t i n g a n d R & D offices a r e very similar. T h e large p e a k s t h a t occ u r r e d in the a c c o u n t i n g o f f i c e were offset b y the p o o r e r v e n t i l a t i o n in the R & D a r e a . T h e engineering office exh i b i t e d a h i g h e r a v e r a g e c o n c e n t r a t i o n t h a n either o f the o t h e r areas. T h e d a y t i m e a v e r a g e in the engineering office w h e n the s m o k e r was a b s e n t was c o m p a r a b l e to c o n c e n t r a t i o n s in b o t h o f the o t h e r offices. T h e engineering o f f i c e also e x h i b i t e d the largest v a r i a t i o n in con-
secutive c o n c e n t r a t i o n m e a s u r e m e n t s d u e to the close proximity of a smoker.
Conclusions
The diurnal respirable aerosol mass concentration p a t t e r n s in offices can easily be m e a s u r e d with the a u t o m a t i c v i b r a t i n g piezoelectric q u a r t z crystal m i c r o b a l a n c e t e c h n i q u e . T h e increases a n d decreases in m a s s
300 i 250-
~
200
I'-" Z 150 UJ Z O O lOO (n u) =f
50
1200 0 2 9 JUNE
MON
0000
1200 3 0 JUNE
TUE
0000
1200 1 JULY
WED
O000
1200 2 JULY
THU
0OO0
1200 3 JULY
FRI
0OO0
1200 4 JULY
SAT
Fig. 4. Aerosol mass concentration in engineering office. A smoker's office was nearby. The smoker was absent on 1 July, 3 July was a holiday, and 4 July was a nonworking Saturday.
Measurement of aerosol concentrations
227
Table 1. Average measured respirable concentrations for three offices during daytime periods. Day
Accounting
R&D
Engineering
1
39 46 39 54 46 45 #g/m ~
37 50 49 46 42 45 #g/m 3
77 89 42 62 -67.5 ~g/m 3
2 3 4 5 Average
concentration are often readily identifiable. The causes of high concentrations are also identifiable by documenting the operations pertinent to the measurement, i.e., a smoker being present during a measurement period. This instrument will undoubtedly be used as a powerful tool in the measurement and documentation of respirable aerosol mass concentrations in offices, homes, work places, and other indoor environments.
References Fairchild, C. I., Tillery, M. I., and Ettinger, H. J. (1980) An evaluation of fast response aerosol mass monitors. Report No. LA-8220, Los Alamos Scientific Laboratory, Los Alamos, NM. Sem. G. J. and Quant, F. R. (in press) An automatic piezobalance respirable aerosol mass monitor for unattended real-time measurements, in Aerosols in the Mining and Industrial Work Environment. Vol. II1: Instrumentation, V. A. Marple and B. Y. H. Liu, eds. Ann Arbor Science, Ann Arbor, MI. Sem, G. J. and Tsurubayashi, K. (1975) A new mass sensor for respirable dust measurement, Am. Ind. Hyg. Assoc. J. 36, 791800. Sem, G. J., Tsurubayashi, K., and Homma, K. (1977) Performance of the piezoelectric microbalance respirable aerosol sensor, Am. Ind. Hyg. Assoc. J. 38, 580-588. Tsurubayashi, K. and Kano, H. (1980) Field testing of automatic piezoelectric microbalances for outdoor aerosol mass concentration measurements, EPA-600/9-80-004, Proceedings: Advances in Particle Sampling and Measurement, W. B. Smith, ed. pp. 217-241. Daytona Beach, FL, October 1979. Tsurubayashi, K., Kano, H., and Hayakawa, I. (in press) Mass concentration measurement by piezobalance dust meters, in Aerosols in the Mining and Industrial Work Environment. Vol. III: Instrumentation, V. A. Marple and B. Y. H. Liu, eds. Ann Arbor Science, Ann Arbor, MI.