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Hourly measurement of particulate concentrations with streaker samplers and optical methods
Nuclear Instruments and Methods in Physics Research B 150 (1999) 370±374
Hourly measurement of particulate concentrations with streaker samplers and optical methods E. Filippi a, P. Prati a b
a,*
, A. Zucchiatti a, F. Lucarelli b, V. Ariola a, P. Corvisiero
a
Dipartimento di Fisica and INFN, via Dodecaneso 33, 16146 Genova, Italy Dipartimento di Fisica and INFN, Largo E. Fermi 2, 50125 Firenze, Italy
Abstract We have studied the possibility of continuous particulate monitoring, by an optical system, on the ®lters of a twostage streaker sampler. The streaker deposits, collected for PIXE analysis, have been examined o-line by measuring the attenuation of a light beam. The optical analysis provides, in a few minutes, an estimate of hourly total mass concentrations, over a one week period, for both stages, very useful as a selection for further PIXE irradiation. We describe the set-up and the calibration procedures, where PIXE plays a fundamental role in resolving dierent aerosol compositions and in validating the prototype performance. The results obtained over 2 weeks of operation and the comparison with the aerosol component determined via PIXE analysis, are also discussed. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 07.88; 82.70.K Keywords: Aerosol; PIXE
1. Introduction Aerosol samplers are usually present in the air quality monitoring networks operating in many towns. While gaseous pollutants are monitored in real-time on a hourly basis, particulate matter is collected for periods ranging from a day to several weeks and analysed o-line, on a daily basis. We have usually triggered accurate particulate PIXE analyses by the real-time observation of
* Corresponding author. Tel.: +39-10-353-6439; fax: +39-10314-218; e-mail: [email protected]
large gaseous component variations. However, the availability of prompt suspended particulate data could improve substantially the picture that one has on pollution episodes in complex urban environments. Some devices are now commercially available [1±3] to provide on-line particulate mass concentration. Unfortunately, they accumulate the particulate matter on media that are often incompatible with PIXE continuous analyses. We describe here a study based on a two-stage streaker sampler [4] and on o-line optical determination of the deposited particulate thickness, in order to assess the requirements for a possible combination of two complementary measurements
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 1 0 7 5 - 1
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
on the same ®lter: semi-quantitative mass concentration and PIXE elemental concentrations. 2. Material and methods The streaker sampler [4] and the control unit that we developed for it, have been described elsewhere [5]. Brie¯y, a streaker consists of a preimpactor that stops particles with diameters greater than 10 lm, of a thin Kapton ®lm that collects particles with an aerodynamic diameter (Dae , in the following) between 2.5 and 10 lm (coarse stage) and a Nuclepore ®lter that stops all smaller particles (®ne stage) with eciency very close to 1. The impaction plate and the ®lter are paired onto a cartridge which rotates continuously for a week, driven by a 12 V DC motor. The sampling produces therefore a circular deposit (``streak'') on the two stages. Air ¯ow through the streaker must be kept around 1 l/min. In our prototype, a 1 mm circular light beam has been produced, starting from a 50 W collimated halogen lamp, and driven through the streak and then to a photodiode (PD) to measure its attenuation. The beam size corresponds to one hour of aerosol sampling. The PD is mounted in a metallic case, it has a square active surface of 5.8 mm2 , a photosensitivity of about 0.14 A/W between 190 and 340 nm and it is positioned 5 mm beyond the streaker stage. The PD output is driven to a Current to Voltage Converter in order to provide a low value of load resistance and to have a linear relationship between incident intensity and PD output. Finally, the CVC output is read by a Keitley 2100, 71=2 digits multimeter with a sensitivity of 0.1 lV. The streaker stages are mounted on the shaft of a stepping motor with a step angle of 1.8° and an angular accuracy of 5%. Each step corresponds to 50 min of aerosol sampling. The multimeter read-out is transmitted, via an IEEE488 port, to a Macintosh IIci computer which also controls the stepping motor. A program, developed in the Labview 4 platform, controls the measurement: in each point of the streak, an average of 5 readings of the multimeter is calculated. Afterwards a pulse to the stepping motor rotates the streak to the next position. The analysis of a
371
streak, corresponding to one week of sampling (168 h), requires 5 min. The light source, the stepping motor and the photodiode are aligned on an optical rail inside a black box. We have bombarded the streaker stages and other ®lters used to calibrate the prototype, with 3 MeV protons at the INFN Van de Graa accelerator in the Physics Department of the University of Florence. This is an external beam facility already used for aerosol analysis [6]. We have adopted a 1 ´ 3 mm2 rectangular beam spot with an intensity ranging from 5 to 15 nA. With the streaker stages, the beam moved along the streak in steps of 1.25 mm corresponding to 1 h of aerosol sampling. Details on the PIXE set-up are reported elsewhere [5,6]. Spectra were ®tted using the GUPIX software package [7] running on a Pentium II, 233 MHz, PC. 3. Results Devices for determination of light attenuation properties of aerosols, with accuracy down to 1%, have been developed in the past [8,9]. Our prototype has, for the moment, lower precision but provides a fast picture of the aerosol concentration time trend and keeps intact the possibility of oline analyses. Although the prototype has been extensively checked from the optical point of view (sources stability, light attenuation through different materials, laser or lamp light source, etc.), we focus here our attention on the role of PIXE in its calibration and on the comparison between PIXE and optical analysis of the streaker stages. Attenuation of light through a medium is the result of both scattering and absorption processes and the light attenuation is generally described by a simple exponential relation: I I0 eÿlx ; where x is the medium thickness, l the attenuation coecient (which is a function to the wavelength), I0 and I the intensity of incident and transmitted light, respectively. We de®ned I0 as the light transmitted by a blank, unexposed ®lter. We veri®ed that the output of the CVC was always proportional to the light intensity impinging on the
372
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
photodiode and therefore we used the ratio V/V0 instead of I/I0 . A series of measurements performed on dierent kinds of blank ®lters (Nuclepore and Kapton stages of streakers, circular Nuclepore and cellulose acetate ®lters) revealed that the apparatus sensitivity, de®ned as the minimum detectable value of the ln(V0 /V), is 0.02. To establish a relationship between thickness of the particulate matter and light attenuation, we prepared a set of 18 samples by pumping, through Nuclepore circular ®lters, dierent quantities of air in three sites (labelled A,B,C) in the town of Genova. The deposit thickness was determined by weighing the ®lters before and after sampling (sensitivity: 0.1 mg). The deposits ranged from 20 to 230 lg/cm2 , which is the interval of values expected for the deposit on streaker stages in a polluted environment [5,10]. To the 18 samples, we added 12 more ®lters, made by cellulose acetate, of the same dimension, chosen from the set of samples collected by the network of air quality monitoring of the town of Genova. In this case, deposit thickness ranged from 110 to 340 lg/cm2 . Actually, we used samples collected in 8 dierent sites in town. Since all the calibration samples were collected without any kind of selection on the particulate diameter we checked the deposition homogeneity by PIXE. The results for one of the Nuclepore ®lters are shown in Fig. 1. The deposit is uniform within 15% showing random ¯uctuations not ordered in position, dierent for each element and probably related to the presence of particulate matter with large diameter. In fact, similar tests performed in the past on the deposition of the streaker stages [11], where particles with Dae >10 lm were ``cut'' by a pre-impactor, gave a deposition uniformity within a few per cent. After the PIXE analysis we decided to measure, for each ®lter, the quantity ln(V0 /V) in 16 points regularly spaced, in a 2 cm wide zone, around the ®lter centre. The average ln(V0 /V) value, used for the calibration, is thus expected to have an error lower than 10%. In Fig. 2, the particulate average composition, measured by PIXE on the set of 12 Nuclepore ®lters, is shown. In site A, the particulate composition is mainly related to the near-large steelsmelter. Site B shows, in addition, a large trac
Fig. 1. Radial distribution of the deposit thickness (normalized to average values) for S (white circle), Fe (black square), Zn (white square), Pb (cross) and the sum of elements (thick line) detected by PIXE in one of the Nuclepores ®lters used for the calibration.
Fig. 2. Mass distribution of the most abundant elements detected by PIXE in the sites where the Nuclepore calibration ®lters were sampled. Site A: neighbourhood of a steel-smelter, Site B: road, Site C: green area.
component since it was located on a busy road not far from the smelter. Site C was a quite clean, green area in the residential part of the town and the aerosol composition is characterized by a signi®cantly lower content in Fe and a higher percentage of Si, S and Ca. The ®lters in cellulose acetate were all sampled in polluted areas of town but we could not perform the PIXE analysis on them. In conclusion, we had most of the calibration ®lters sampled near industrial plants or heavy
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
373
tracked roads with 7 ®lters coming from a green area (site C). In Fig. 3(a), the ln(V0 /V) is plotted against the deposit thickness (determined by weighing) on the whole set of 30 calibration ®lters. The best ®t curve, determined by the least squares method, has a regression coecient of 0.75 and the slope, which gives the average value for l, 0.0060 + 0.0002 cm2 / lg. The scattering of the data around the ®t, probably due to the variation in the aerosol composition and therefore in its attenuation properties, shows anyway that prediction on the aerosol concentration are possible, in our case, within a factor of 2. A better result can be obtained if, from the calibration ®lters set, the 7 samples coming from the green area (site C) are discarded. These represent most of the points lying below the best ®t curve shown in Fig. 3(a). With this reduced set (Fig. 3(b)), the best ®t curve has a regression co-
ecient of 0.87 while the slope turns out to be 0.0068 + 0.0003 cm2 /lg. Taking into account the calibration curve, the apparatus sensitivity is given by: xmin ln(V0 /V)min /l 0.02/0.0068 3 lg/cm2 . In Fig. 4, the results of the scanning of some streaker stages (Nuclepore and Kapton) with the proton beam (PIXE) and with our prototype (where l 0.0068 cm2 /lg was used) are compared. The sampling lasted for 2 weeks of Winter 1997 in the proximity of a steel-smelter located in the town of Genova. The PIXE analysis is able to detect about 10% and 30% of the total aerosol mass in the ®ne and coarse stage, respectively. Moreover, the two methods produce almost correlated time series with the only exception of a few hours around day 9 in the ®ne stage and between days 3 and 6 in the coarse stage (see Fig. 4). In the coarse
Fig. 3. Light attenuation versus the deposit thickness of the calibration ®lters. Full squares: Nuclepore ®lters, White circles: Cellulose acetate ®lters. Panel a: all the calibration ®lters; panel b: without ®lters sampled in site C.
Fig. 4. Concentration time series (lg/m3 ) measured as the sum of the elements detected by PIXE and by the optical method in the ®ne (top) and coarse (bottom) stage. Full line, left axis: optical method; dotted line, right axis: PIXE.
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E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
stage, the peak not detected by the optical methods are due to sudden increases in the Cl and K concentrations. The correlation coecients, between the concentration series measured by PIXE and our prototype, are around 0.6. This work can give the basis for an extended use of the technique where fast estimate of the aerosol mass concentration and continuous elemental concentrations, determined by PIXE, could be coupled on the same ®lters. While the aerosol mass concentration can be measured only with relatively large uncertainities, its optical properties, which aect, for example, the atmospheric visibility, could be measured with good accuracy. Moreover, in the present con®guration, our prototype can be very useful in extended sampling campaigns with streaker samplers where, for example, it could be used to select the most interesting ®lters for further and more expensive PIXE analysis. References [1] TEOM 1400a Ambient Particulate Monitor manufactured by Rupprecht & atashnick, 25 Corporate Circle, Albany, NY 12203 USA.
[2] GBAM-1020 Beta Attenuation Ambient Particulate Mass Monitor manufactured by Pac Will Environmental, P.O. Box 9124, Hamilton, Ont., Canada L8H 758. [3] DataRAM Portable Real-time Aerosol Monitor, manufactured by MIE, 7 Oak Park Bedford, MA 01730. [4] PIXE International Corp., P.O. Box 7744, Tallahassee, FL 32316, USA. [5] P. Formenti, P. Prati, A. Zucchiatti, F. Lucarelli, P.A. Mand o, Nucl. Instr. and Meth. B 113 (1996) 359±362. [6] P. Del Carmine, F. Lucarelli, P.A. Mand o, G. Moscheni, A. Pecchioli, J.D. MacArthur, Nucl. Instr and Meth. B 45 (1990) 341±346. [7] J.A. Maxwell, W.J. Teesdale, J.L. Campbell, Nucl. Instr. and Meth. B 95 (1995) 407±421. [8] R. Hitzenberger, Aerosol Sci. and Technol. 18 (1993) 70± 84. [9] D. Campbell, S. Copeland, T. Cahill, Aerosol Sci. and Technol. 22 (1995) 287±292. [10] P. Formenti, H.J. Annegarn, P. Prati, A. Zucchiatti, F. Lucarelli, P.A. Mand o, Physica Medica 13 (3) (1997) 101± 109. [11] P. Prati, F. Cardoni, P. Formenti, A. Zucchiatti, F. Lucarelli, P. A. Mand o, E. Cereda, in: J.L. Duggan, I.L. Morgan (Eds.), AIP. Conf. Proc., 1997, CP392, pp. 579± 582.
Hourly measurement of particulate concentrations with streaker samplers and optical methods E. Filippi a, P. Prati a b
a,*
, A. Zucchiatti a, F. Lucarelli b, V. Ariola a, P. Corvisiero
a
Dipartimento di Fisica and INFN, via Dodecaneso 33, 16146 Genova, Italy Dipartimento di Fisica and INFN, Largo E. Fermi 2, 50125 Firenze, Italy
Abstract We have studied the possibility of continuous particulate monitoring, by an optical system, on the ®lters of a twostage streaker sampler. The streaker deposits, collected for PIXE analysis, have been examined o-line by measuring the attenuation of a light beam. The optical analysis provides, in a few minutes, an estimate of hourly total mass concentrations, over a one week period, for both stages, very useful as a selection for further PIXE irradiation. We describe the set-up and the calibration procedures, where PIXE plays a fundamental role in resolving dierent aerosol compositions and in validating the prototype performance. The results obtained over 2 weeks of operation and the comparison with the aerosol component determined via PIXE analysis, are also discussed. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 07.88; 82.70.K Keywords: Aerosol; PIXE
1. Introduction Aerosol samplers are usually present in the air quality monitoring networks operating in many towns. While gaseous pollutants are monitored in real-time on a hourly basis, particulate matter is collected for periods ranging from a day to several weeks and analysed o-line, on a daily basis. We have usually triggered accurate particulate PIXE analyses by the real-time observation of
* Corresponding author. Tel.: +39-10-353-6439; fax: +39-10314-218; e-mail: [email protected]
large gaseous component variations. However, the availability of prompt suspended particulate data could improve substantially the picture that one has on pollution episodes in complex urban environments. Some devices are now commercially available [1±3] to provide on-line particulate mass concentration. Unfortunately, they accumulate the particulate matter on media that are often incompatible with PIXE continuous analyses. We describe here a study based on a two-stage streaker sampler [4] and on o-line optical determination of the deposited particulate thickness, in order to assess the requirements for a possible combination of two complementary measurements
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 1 0 7 5 - 1
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
on the same ®lter: semi-quantitative mass concentration and PIXE elemental concentrations. 2. Material and methods The streaker sampler [4] and the control unit that we developed for it, have been described elsewhere [5]. Brie¯y, a streaker consists of a preimpactor that stops particles with diameters greater than 10 lm, of a thin Kapton ®lm that collects particles with an aerodynamic diameter (Dae , in the following) between 2.5 and 10 lm (coarse stage) and a Nuclepore ®lter that stops all smaller particles (®ne stage) with eciency very close to 1. The impaction plate and the ®lter are paired onto a cartridge which rotates continuously for a week, driven by a 12 V DC motor. The sampling produces therefore a circular deposit (``streak'') on the two stages. Air ¯ow through the streaker must be kept around 1 l/min. In our prototype, a 1 mm circular light beam has been produced, starting from a 50 W collimated halogen lamp, and driven through the streak and then to a photodiode (PD) to measure its attenuation. The beam size corresponds to one hour of aerosol sampling. The PD is mounted in a metallic case, it has a square active surface of 5.8 mm2 , a photosensitivity of about 0.14 A/W between 190 and 340 nm and it is positioned 5 mm beyond the streaker stage. The PD output is driven to a Current to Voltage Converter in order to provide a low value of load resistance and to have a linear relationship between incident intensity and PD output. Finally, the CVC output is read by a Keitley 2100, 71=2 digits multimeter with a sensitivity of 0.1 lV. The streaker stages are mounted on the shaft of a stepping motor with a step angle of 1.8° and an angular accuracy of 5%. Each step corresponds to 50 min of aerosol sampling. The multimeter read-out is transmitted, via an IEEE488 port, to a Macintosh IIci computer which also controls the stepping motor. A program, developed in the Labview 4 platform, controls the measurement: in each point of the streak, an average of 5 readings of the multimeter is calculated. Afterwards a pulse to the stepping motor rotates the streak to the next position. The analysis of a
371
streak, corresponding to one week of sampling (168 h), requires 5 min. The light source, the stepping motor and the photodiode are aligned on an optical rail inside a black box. We have bombarded the streaker stages and other ®lters used to calibrate the prototype, with 3 MeV protons at the INFN Van de Graa accelerator in the Physics Department of the University of Florence. This is an external beam facility already used for aerosol analysis [6]. We have adopted a 1 ´ 3 mm2 rectangular beam spot with an intensity ranging from 5 to 15 nA. With the streaker stages, the beam moved along the streak in steps of 1.25 mm corresponding to 1 h of aerosol sampling. Details on the PIXE set-up are reported elsewhere [5,6]. Spectra were ®tted using the GUPIX software package [7] running on a Pentium II, 233 MHz, PC. 3. Results Devices for determination of light attenuation properties of aerosols, with accuracy down to 1%, have been developed in the past [8,9]. Our prototype has, for the moment, lower precision but provides a fast picture of the aerosol concentration time trend and keeps intact the possibility of oline analyses. Although the prototype has been extensively checked from the optical point of view (sources stability, light attenuation through different materials, laser or lamp light source, etc.), we focus here our attention on the role of PIXE in its calibration and on the comparison between PIXE and optical analysis of the streaker stages. Attenuation of light through a medium is the result of both scattering and absorption processes and the light attenuation is generally described by a simple exponential relation: I I0 eÿlx ; where x is the medium thickness, l the attenuation coecient (which is a function to the wavelength), I0 and I the intensity of incident and transmitted light, respectively. We de®ned I0 as the light transmitted by a blank, unexposed ®lter. We veri®ed that the output of the CVC was always proportional to the light intensity impinging on the
372
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
photodiode and therefore we used the ratio V/V0 instead of I/I0 . A series of measurements performed on dierent kinds of blank ®lters (Nuclepore and Kapton stages of streakers, circular Nuclepore and cellulose acetate ®lters) revealed that the apparatus sensitivity, de®ned as the minimum detectable value of the ln(V0 /V), is 0.02. To establish a relationship between thickness of the particulate matter and light attenuation, we prepared a set of 18 samples by pumping, through Nuclepore circular ®lters, dierent quantities of air in three sites (labelled A,B,C) in the town of Genova. The deposit thickness was determined by weighing the ®lters before and after sampling (sensitivity: 0.1 mg). The deposits ranged from 20 to 230 lg/cm2 , which is the interval of values expected for the deposit on streaker stages in a polluted environment [5,10]. To the 18 samples, we added 12 more ®lters, made by cellulose acetate, of the same dimension, chosen from the set of samples collected by the network of air quality monitoring of the town of Genova. In this case, deposit thickness ranged from 110 to 340 lg/cm2 . Actually, we used samples collected in 8 dierent sites in town. Since all the calibration samples were collected without any kind of selection on the particulate diameter we checked the deposition homogeneity by PIXE. The results for one of the Nuclepore ®lters are shown in Fig. 1. The deposit is uniform within 15% showing random ¯uctuations not ordered in position, dierent for each element and probably related to the presence of particulate matter with large diameter. In fact, similar tests performed in the past on the deposition of the streaker stages [11], where particles with Dae >10 lm were ``cut'' by a pre-impactor, gave a deposition uniformity within a few per cent. After the PIXE analysis we decided to measure, for each ®lter, the quantity ln(V0 /V) in 16 points regularly spaced, in a 2 cm wide zone, around the ®lter centre. The average ln(V0 /V) value, used for the calibration, is thus expected to have an error lower than 10%. In Fig. 2, the particulate average composition, measured by PIXE on the set of 12 Nuclepore ®lters, is shown. In site A, the particulate composition is mainly related to the near-large steelsmelter. Site B shows, in addition, a large trac
Fig. 1. Radial distribution of the deposit thickness (normalized to average values) for S (white circle), Fe (black square), Zn (white square), Pb (cross) and the sum of elements (thick line) detected by PIXE in one of the Nuclepores ®lters used for the calibration.
Fig. 2. Mass distribution of the most abundant elements detected by PIXE in the sites where the Nuclepore calibration ®lters were sampled. Site A: neighbourhood of a steel-smelter, Site B: road, Site C: green area.
component since it was located on a busy road not far from the smelter. Site C was a quite clean, green area in the residential part of the town and the aerosol composition is characterized by a signi®cantly lower content in Fe and a higher percentage of Si, S and Ca. The ®lters in cellulose acetate were all sampled in polluted areas of town but we could not perform the PIXE analysis on them. In conclusion, we had most of the calibration ®lters sampled near industrial plants or heavy
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
373
tracked roads with 7 ®lters coming from a green area (site C). In Fig. 3(a), the ln(V0 /V) is plotted against the deposit thickness (determined by weighing) on the whole set of 30 calibration ®lters. The best ®t curve, determined by the least squares method, has a regression coecient of 0.75 and the slope, which gives the average value for l, 0.0060 + 0.0002 cm2 / lg. The scattering of the data around the ®t, probably due to the variation in the aerosol composition and therefore in its attenuation properties, shows anyway that prediction on the aerosol concentration are possible, in our case, within a factor of 2. A better result can be obtained if, from the calibration ®lters set, the 7 samples coming from the green area (site C) are discarded. These represent most of the points lying below the best ®t curve shown in Fig. 3(a). With this reduced set (Fig. 3(b)), the best ®t curve has a regression co-
ecient of 0.87 while the slope turns out to be 0.0068 + 0.0003 cm2 /lg. Taking into account the calibration curve, the apparatus sensitivity is given by: xmin ln(V0 /V)min /l 0.02/0.0068 3 lg/cm2 . In Fig. 4, the results of the scanning of some streaker stages (Nuclepore and Kapton) with the proton beam (PIXE) and with our prototype (where l 0.0068 cm2 /lg was used) are compared. The sampling lasted for 2 weeks of Winter 1997 in the proximity of a steel-smelter located in the town of Genova. The PIXE analysis is able to detect about 10% and 30% of the total aerosol mass in the ®ne and coarse stage, respectively. Moreover, the two methods produce almost correlated time series with the only exception of a few hours around day 9 in the ®ne stage and between days 3 and 6 in the coarse stage (see Fig. 4). In the coarse
Fig. 3. Light attenuation versus the deposit thickness of the calibration ®lters. Full squares: Nuclepore ®lters, White circles: Cellulose acetate ®lters. Panel a: all the calibration ®lters; panel b: without ®lters sampled in site C.
Fig. 4. Concentration time series (lg/m3 ) measured as the sum of the elements detected by PIXE and by the optical method in the ®ne (top) and coarse (bottom) stage. Full line, left axis: optical method; dotted line, right axis: PIXE.
374
E. Filippi et al. / Nucl. Instr. and Meth. in Phys. Res. B 150 (1999) 370±374
stage, the peak not detected by the optical methods are due to sudden increases in the Cl and K concentrations. The correlation coecients, between the concentration series measured by PIXE and our prototype, are around 0.6. This work can give the basis for an extended use of the technique where fast estimate of the aerosol mass concentration and continuous elemental concentrations, determined by PIXE, could be coupled on the same ®lters. While the aerosol mass concentration can be measured only with relatively large uncertainities, its optical properties, which aect, for example, the atmospheric visibility, could be measured with good accuracy. Moreover, in the present con®guration, our prototype can be very useful in extended sampling campaigns with streaker samplers where, for example, it could be used to select the most interesting ®lters for further and more expensive PIXE analysis. References [1] TEOM 1400a Ambient Particulate Monitor manufactured by Rupprecht & atashnick, 25 Corporate Circle, Albany, NY 12203 USA.
[2] GBAM-1020 Beta Attenuation Ambient Particulate Mass Monitor manufactured by Pac Will Environmental, P.O. Box 9124, Hamilton, Ont., Canada L8H 758. [3] DataRAM Portable Real-time Aerosol Monitor, manufactured by MIE, 7 Oak Park Bedford, MA 01730. [4] PIXE International Corp., P.O. Box 7744, Tallahassee, FL 32316, USA. [5] P. Formenti, P. Prati, A. Zucchiatti, F. Lucarelli, P.A. Mand o, Nucl. Instr. and Meth. B 113 (1996) 359±362. [6] P. Del Carmine, F. Lucarelli, P.A. Mand o, G. Moscheni, A. Pecchioli, J.D. MacArthur, Nucl. Instr and Meth. B 45 (1990) 341±346. [7] J.A. Maxwell, W.J. Teesdale, J.L. Campbell, Nucl. Instr. and Meth. B 95 (1995) 407±421. [8] R. Hitzenberger, Aerosol Sci. and Technol. 18 (1993) 70± 84. [9] D. Campbell, S. Copeland, T. Cahill, Aerosol Sci. and Technol. 22 (1995) 287±292. [10] P. Formenti, H.J. Annegarn, P. Prati, A. Zucchiatti, F. Lucarelli, P.A. Mand o, Physica Medica 13 (3) (1997) 101± 109. [11] P. Prati, F. Cardoni, P. Formenti, A. Zucchiatti, F. Lucarelli, P. A. Mand o, E. Cereda, in: J.L. Duggan, I.L. Morgan (Eds.), AIP. Conf. Proc., 1997, CP392, pp. 579± 582.