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Deposition of indoor aerosols as determined by PIXE analysis
Nuclear Instruments and Methods North-Holland. Amsterdam
DEPOSITION Markku
OF INDOOR
KULMALA,
Taisto
in Physics
Research
AEROSOLS
B22 (1987)
AS DETERMINED
RAUNEMAA*
and Unto
University of Helsinki, Department of Physics, Siltavuorenpenger
337
337-339
BY PIXE ANALYSIS
TAPPER
20 D, 00170 Helsinki. Finland
In indoor air the main deposition mechanisms are sedimentation on horizontal surfaces, diffusion on vertical and horizontal surfaces and electrical interaction. In our study the deposition coupons (three different types) were situated in different locations in a room, Four coupons were placed on a vertical plane and six on a horizontal plane at a height of 5-190 cm. Simultaneously, suspended particles were collected by 2-fraction filter collectors. The average airborne concentrations and surface accumulations were analyzed by the internal beam PIXE facility. Final results were calculated for ten elements. The sulphur concentrations were also analyzed by ion-chromatography. The results were in good agreement with the PIXE values. This deposition study is a part of successive investigations. where the behaviour of indoor aerosols are studied.
1. Introduction The indoor air particle concentration can be described by a model including the particle production rate from indoor sources, ventilation and deposition rates, and mechanical filtration in air-conditioning. Deposition rates onto horizontal and vertical surfaces were investigated in this study. A multielemental database on indoor air concentrations is also necessary. Such a database was tried to be achieved by filter collection and PIXE analysis. In our laboratory the PIXE technique has been developed during the last ten years, the main interest being in the application on aerosol research.
2. Experimental 2.1.
Deposition
methods measurements
When indoor particle depositions are considered several factors must be taken into account. These are summarized in the table 1. The interaction of the factors listed in table 1 can be described by the formula (omitting the subscripts) [ 11: dlidt
= q + l(s0
- I) - al.
* Present address: University of Kuopio, Department of Environmental Hygiene, POB 6. 70211 Kuopio. Finland.
B.V.
particle
Outdoor particle concentration Indoor particle concentration Emission rate for an indoor source
Ventilation rate Filtration efficiency factor Deposition rate
deposition
(applic-
0, 4
4, 1, $8 a1
Three different types of coupons (Al-Mylar foil, Apiezon Nuclepore membrane filter and a special electricity filter, FiltreteTM) were used. From these the Apiezon Nuclepore filter proved to be the most suitable for collection. The deposition coupons (10 of each type) were attached to holders and then situated onto vertical (4 coupons) and horizontal (6 coupons) surfaces at heights of 5 to 190 cm above the floor level. Particles were collected for 2 weeks (in 3 locations) and for 4 weeks (7 locations). Suspended particles were measured during this period by using 2-fraction filter collection [4]. After collection deposition coupons and filters were weighed and analyzed by the internal beam PIXE facility [2]. 2.2.
The deposition velocities and rates were determined in a dwelling house environment. The experimental values were measured indirectly by using deposition coupons situated horizontally as well as vertically.
0168-583X187/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
Table 1 Factors playing a role in indoor able for each substance i).
PIXE measurements
The 3 MeV proton beam of the 5 MV tandem Van de Graaff generator at the University of Helsinki was used in the analysis. The proton current varied from 10 to 20 nA. The backscattered protons were monitored by a surface barrier detector for current normalization. The 3 MeV proton beam was accessed into the evacuated target chamber through a 2.5 pm nickel III.
ATMOSPHERIC
APPLICATIONS
M. Kulmala et al. I Deposition
33x
Table 2 The comparison of sulphur concentrations measured means of the PIXE method and ion-chromatography Filter number
PIXE
Ion-chromatography
(&cm-)
(Mcm’)
1YYA 203A 202A 1YXA 206A 215A 268B
3.3 3.0 2.3 2.4 1.7 1.3 0
3.1 3.1 2.2 2.2 1.3 0.95 0
of indoor
air aerosols
by
exit foil. The X-rays were detected with a SO mm’ x 5 mm Si(Li) detector connected to a Silena 8192 channel analyzer and a PDP 11144 computer. The spectra were analyzed by using the program HHEX. Concentrations of 10 elements from silicon on were detected, the minimum detection limit being 20 ng/cm’. Because sulphur is an interesting element in many fields of aerosol research and also indoors, the sulphur concentration in some samples was detected with ionchromatography too. The results were in good agreement with our PIXE results (table 2).
1
da--
9pm
0 Fine
600 Total
1000 concentratiop
(ng/m3
1
Fig. 1. The measured surface accumulation rates as a function of the total concentration. The lines show the theoretical surface accumulation rates for particles with aerodynamic diameters of 0.5, 3, 6 and Y Km.
3. Results From the elemental concentrations the mean surface accumulation rates were calculated for ten elements (Si, S, Cl, Ca, Ti. Fe, Ni, Cu, and Zn) and for total mass. The deposition velocity u, was calculated using the formula: v, = DII , where D is the deposition flux onto the surface and I the total concentration for a particular element. From the deposition velocity the deposition rate can be estimated by a=v,,AlV.
where A is the total deposition area and V the volume of the room. In fig. 1 is presented the average surface accumulation rate for different elements as a function of the total concentration. Interestingly. it was found that sulphur behaved differently to other elements. The particles containing sulphur were suspended much longer than the other particles. In fig. 2 the deposition velocity as a function of the aerodynamic diameter is shown. According to the present measurements the deposition velocity for sulphur particles is found to be about 0.003 cm/s. The respective value for all particles was 0.25 cm/s. These values correspond to an aerodynamic mass median
10-l Aerodynamic
1
10 diameter
102 d,
( pm)
Fig. 2. Deposition velocity as a function of the aerodynamic diameter. The points are from the present measurements and also a theoretical curve is shown.
diameter of approximately 8 pm for all deposited particles as compared to 0.5 pm for sulphur particles. The fact that the sulphur concentration seems to correspond mainly to the smaller particles was supported by measurements where the effect of ventilation and mechanical filtration in air conditioning systems was studied. It was found that the sulphur particles seem to be able to penetrate the filtration units much easier than other particles [4]. In fig. 3 is shown the fine fraction results for sulphur
M.
Kuinuda
I (ng/m3)
V
0
et ul.
I Deposition
/
I
I
500
1000
*
0 (ng/m3)
Fig. 3. Fine fraction indoor sulphur concentrations versus outdoor concentrations. Also the effect of the ventilation rate is shown. The lines show the calculated indoor sulphur concentrations when the ventilation rate is 0.5 h- ’ (lower line) and 0.3 h-’ (upper line). Cr Co CI K
51 Ca M
Fe S
Ti Zn Ni Pb Dis
339
of indoor air aerosols
The evaluation of the influence of different sources on experimental aerosol concentrations is an experimental as well as a statistical problem. As PIXE affords a reliable multielemental database on aerosol concentrations, a statistical procedure can be applied to the data. When using a cluster analysis, a variation of the multivariate technique. the elemental results can be classified into clusters. In fig. 4 such a classihcation of deposition data is shown. The elements Si, Cl, K, Ca and Fe form a cluster with the total mass whereas sulphur and titanium are clustered together. From the fig. 2 titanium and sulphur can be estimated to exist in small particles and elements in the other cluster in large particles.
4. Discussion The results for the deposition velocities by using the PIXE technique in the deposition coupon analysis are similar to those in the literature [3]. In the present work, however, several elemental deposition rates can be obtained with high sensitivity. Thus, a wide analysis of deposition characteristics can be achieved. This is mainly due to ultimate capabilities of PIXE.
References -1.0
Fig. 4. A cluster analysis of the present deposition data. M is the total mass concentration and DIS corresponds to vertical distance from the floor level. Other symbols refer to elemental concentrations. The line represents 99% confidence level. concentrations indoors versus the results for outdoor concentrations. The effect of the ventilation rate is also shown. The theoretical lines are calculated assuming a value of 0.2 h-’ for the deposition rate for sulphur particles. The measurements are in good agreement with the theoretical results.
[If
M. Olin. The Model for Indoor Air Aerosols. Internal Report. Department of Physics, University of Helsinki (1986), in Finnish. PI T. Raunemaa. M. Vaittinen, J. Ratsanen, T. Tuomi and M. Gerlander. Nucl. Instr. and Meth. 181 (1981) 43. Sinclair, LA. Psota-Kelty and C.J. Weschler, [31 J.D. Atmos. Environ 1Y (1985) 315. M. Kulmala, K. Karhula, V. Riihiluoma. [41 T. Raunemaa, J. Jokiniemi and A. Reponen, Indoor Air Aerosols and their Dependence on Outdoor Concentrations, Internal Report, Department of Physics, University of Helsinki (1984) in Finnish.
III.
ATMOSPHERIC
APPLICATIONS
DEPOSITION Markku
OF INDOOR
KULMALA,
Taisto
in Physics
Research
AEROSOLS
B22 (1987)
AS DETERMINED
RAUNEMAA*
and Unto
University of Helsinki, Department of Physics, Siltavuorenpenger
337
337-339
BY PIXE ANALYSIS
TAPPER
20 D, 00170 Helsinki. Finland
In indoor air the main deposition mechanisms are sedimentation on horizontal surfaces, diffusion on vertical and horizontal surfaces and electrical interaction. In our study the deposition coupons (three different types) were situated in different locations in a room, Four coupons were placed on a vertical plane and six on a horizontal plane at a height of 5-190 cm. Simultaneously, suspended particles were collected by 2-fraction filter collectors. The average airborne concentrations and surface accumulations were analyzed by the internal beam PIXE facility. Final results were calculated for ten elements. The sulphur concentrations were also analyzed by ion-chromatography. The results were in good agreement with the PIXE values. This deposition study is a part of successive investigations. where the behaviour of indoor aerosols are studied.
1. Introduction The indoor air particle concentration can be described by a model including the particle production rate from indoor sources, ventilation and deposition rates, and mechanical filtration in air-conditioning. Deposition rates onto horizontal and vertical surfaces were investigated in this study. A multielemental database on indoor air concentrations is also necessary. Such a database was tried to be achieved by filter collection and PIXE analysis. In our laboratory the PIXE technique has been developed during the last ten years, the main interest being in the application on aerosol research.
2. Experimental 2.1.
Deposition
methods measurements
When indoor particle depositions are considered several factors must be taken into account. These are summarized in the table 1. The interaction of the factors listed in table 1 can be described by the formula (omitting the subscripts) [ 11: dlidt
= q + l(s0
- I) - al.
* Present address: University of Kuopio, Department of Environmental Hygiene, POB 6. 70211 Kuopio. Finland.
B.V.
particle
Outdoor particle concentration Indoor particle concentration Emission rate for an indoor source
Ventilation rate Filtration efficiency factor Deposition rate
deposition
(applic-
0, 4
4, 1, $8 a1
Three different types of coupons (Al-Mylar foil, Apiezon Nuclepore membrane filter and a special electricity filter, FiltreteTM) were used. From these the Apiezon Nuclepore filter proved to be the most suitable for collection. The deposition coupons (10 of each type) were attached to holders and then situated onto vertical (4 coupons) and horizontal (6 coupons) surfaces at heights of 5 to 190 cm above the floor level. Particles were collected for 2 weeks (in 3 locations) and for 4 weeks (7 locations). Suspended particles were measured during this period by using 2-fraction filter collection [4]. After collection deposition coupons and filters were weighed and analyzed by the internal beam PIXE facility [2]. 2.2.
The deposition velocities and rates were determined in a dwelling house environment. The experimental values were measured indirectly by using deposition coupons situated horizontally as well as vertically.
0168-583X187/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
Table 1 Factors playing a role in indoor able for each substance i).
PIXE measurements
The 3 MeV proton beam of the 5 MV tandem Van de Graaff generator at the University of Helsinki was used in the analysis. The proton current varied from 10 to 20 nA. The backscattered protons were monitored by a surface barrier detector for current normalization. The 3 MeV proton beam was accessed into the evacuated target chamber through a 2.5 pm nickel III.
ATMOSPHERIC
APPLICATIONS
M. Kulmala et al. I Deposition
33x
Table 2 The comparison of sulphur concentrations measured means of the PIXE method and ion-chromatography Filter number
PIXE
Ion-chromatography
(&cm-)
(Mcm’)
1YYA 203A 202A 1YXA 206A 215A 268B
3.3 3.0 2.3 2.4 1.7 1.3 0
3.1 3.1 2.2 2.2 1.3 0.95 0
of indoor
air aerosols
by
exit foil. The X-rays were detected with a SO mm’ x 5 mm Si(Li) detector connected to a Silena 8192 channel analyzer and a PDP 11144 computer. The spectra were analyzed by using the program HHEX. Concentrations of 10 elements from silicon on were detected, the minimum detection limit being 20 ng/cm’. Because sulphur is an interesting element in many fields of aerosol research and also indoors, the sulphur concentration in some samples was detected with ionchromatography too. The results were in good agreement with our PIXE results (table 2).
1
da--
9pm
0 Fine
600 Total
1000 concentratiop
(ng/m3
1
Fig. 1. The measured surface accumulation rates as a function of the total concentration. The lines show the theoretical surface accumulation rates for particles with aerodynamic diameters of 0.5, 3, 6 and Y Km.
3. Results From the elemental concentrations the mean surface accumulation rates were calculated for ten elements (Si, S, Cl, Ca, Ti. Fe, Ni, Cu, and Zn) and for total mass. The deposition velocity u, was calculated using the formula: v, = DII , where D is the deposition flux onto the surface and I the total concentration for a particular element. From the deposition velocity the deposition rate can be estimated by a=v,,AlV.
where A is the total deposition area and V the volume of the room. In fig. 1 is presented the average surface accumulation rate for different elements as a function of the total concentration. Interestingly. it was found that sulphur behaved differently to other elements. The particles containing sulphur were suspended much longer than the other particles. In fig. 2 the deposition velocity as a function of the aerodynamic diameter is shown. According to the present measurements the deposition velocity for sulphur particles is found to be about 0.003 cm/s. The respective value for all particles was 0.25 cm/s. These values correspond to an aerodynamic mass median
10-l Aerodynamic
1
10 diameter
102 d,
( pm)
Fig. 2. Deposition velocity as a function of the aerodynamic diameter. The points are from the present measurements and also a theoretical curve is shown.
diameter of approximately 8 pm for all deposited particles as compared to 0.5 pm for sulphur particles. The fact that the sulphur concentration seems to correspond mainly to the smaller particles was supported by measurements where the effect of ventilation and mechanical filtration in air conditioning systems was studied. It was found that the sulphur particles seem to be able to penetrate the filtration units much easier than other particles [4]. In fig. 3 is shown the fine fraction results for sulphur
M.
Kuinuda
I (ng/m3)
V
0
et ul.
I Deposition
/
I
I
500
1000
*
0 (ng/m3)
Fig. 3. Fine fraction indoor sulphur concentrations versus outdoor concentrations. Also the effect of the ventilation rate is shown. The lines show the calculated indoor sulphur concentrations when the ventilation rate is 0.5 h- ’ (lower line) and 0.3 h-’ (upper line). Cr Co CI K
51 Ca M
Fe S
Ti Zn Ni Pb Dis
339
of indoor air aerosols
The evaluation of the influence of different sources on experimental aerosol concentrations is an experimental as well as a statistical problem. As PIXE affords a reliable multielemental database on aerosol concentrations, a statistical procedure can be applied to the data. When using a cluster analysis, a variation of the multivariate technique. the elemental results can be classified into clusters. In fig. 4 such a classihcation of deposition data is shown. The elements Si, Cl, K, Ca and Fe form a cluster with the total mass whereas sulphur and titanium are clustered together. From the fig. 2 titanium and sulphur can be estimated to exist in small particles and elements in the other cluster in large particles.
4. Discussion The results for the deposition velocities by using the PIXE technique in the deposition coupon analysis are similar to those in the literature [3]. In the present work, however, several elemental deposition rates can be obtained with high sensitivity. Thus, a wide analysis of deposition characteristics can be achieved. This is mainly due to ultimate capabilities of PIXE.
References -1.0
Fig. 4. A cluster analysis of the present deposition data. M is the total mass concentration and DIS corresponds to vertical distance from the floor level. Other symbols refer to elemental concentrations. The line represents 99% confidence level. concentrations indoors versus the results for outdoor concentrations. The effect of the ventilation rate is also shown. The theoretical lines are calculated assuming a value of 0.2 h-’ for the deposition rate for sulphur particles. The measurements are in good agreement with the theoretical results.
[If
M. Olin. The Model for Indoor Air Aerosols. Internal Report. Department of Physics, University of Helsinki (1986), in Finnish. PI T. Raunemaa. M. Vaittinen, J. Ratsanen, T. Tuomi and M. Gerlander. Nucl. Instr. and Meth. 181 (1981) 43. Sinclair, LA. Psota-Kelty and C.J. Weschler, [31 J.D. Atmos. Environ 1Y (1985) 315. M. Kulmala, K. Karhula, V. Riihiluoma. [41 T. Raunemaa, J. Jokiniemi and A. Reponen, Indoor Air Aerosols and their Dependence on Outdoor Concentrations, Internal Report, Department of Physics, University of Helsinki (1984) in Finnish.
III.
ATMOSPHERIC
APPLICATIONS