Environ. Scl. Technol. 1986, 2 0 , 1257-1259
(14) Bruner, F.; Bertoni, G.; Crescentini,G. J. Chromatogr. 1978, 167, 399-407. (15) Vidal-Madjar,C.; Gonnord, M. F.; Benchah, F.; Guiochon, G. J. Chromatogr. Sci. 1978, 16, 190-196. (16) Hubbard, S.; Russwurm, G. M.; Walburn, S. G. Atmos. Enuiron. 1981, 15, 905-908. (17) Kissa, E. Anal. Chem. 1983, 55, 1222-1225. (18) Wickbold, R. Angew. Chem. 1952,64,133-135.
(19) Wickbold, R. Angew. Chem. 1954,66, 173. (20) Sweetser, P. B. Anal. Chem. 1956,28, 1766-1768. (21) Kissa, E. Anal. Chem. 1983,55, 1445-1448. (22) Gregory, E. D.; Elia, V. J. Am. Znd. Hyg. Assoc. J. 1983, 44, 88-96. Received for review April 21, 1986. Accepted August 14, 1986.
NOTES Radioactivity Size Distributions of Ambient Aerosols in Helsinki, Finland, during May 1986 after the Chernobyl Accident: Preliminary Report Esko I. Kaupplnen" Laboratory of Heating and Ventilating, Technical Research Centre of Finland, SF-021 50 Espoo, Finland
Rlsto E. Hlllamo Air Quality Department, Finnish Meteorological Institute, SF-0081 0 Helsinki, Finland
S. Hannele Aaltonen and Kari 1.S. Sinkko Surveillance Department, Finnish Centre for Radiation and Nuclear Safety, SF-00 10 1 Helsinki, Finland ~
Ambient aerosol size distributions of 1311,lo3Ru,132Te, and 13'Cs radionuclides were measured in Helsinki, Finland, during May 7-14, 1986. Radioactivity size distributions were unimodal. The geometric mean diameter of 1311was in the size range 0.33-0.57 p m a.e.d. Other isotopes had geometric mean diameters in the size range 0.65-0.93 pm a.e.d. Introduction
Following the accident at Chernobyl nuclear power station on April 26, 1986, great amounts of radioactive aerosols were emitted into the troposphere. Particle size distributions of radioactive isotopes should be known, in order to understand and to be able to predict the behavior, transport, and deposition of radioactive material. In this report, preliminary results of ambient radioactive aerosol size distribution measurements during May 7-14 in Helsinki, Finland, are given. Experimental Methods
Sampling. Aerosol samples were collected with 11-stage multijet compressible flow low-pressure impactors (modified HAUKE 25/0.015 LPI) covering 0.03-16-pm aerodynamic diameter size range (1-3). A Liu-type aerosol inlet was connected to the LPI inlet to minimize the effect of wind on the aspiration efficiency ( 4 ) . Polycarbonate films of 10-pm thickness were used as impaction substrates. To prevent coarse-particle bounce, the films on the stages collecting particles greater than 1 pm a.e.d. were greased thinly with a uniform layer of Apiezon L-grease. The amount of grease on the film was 30-300 pg. Samples were collected during May 7-14,1986. Sampling periods are given in Table I. Weather conditions and air trajectories are given elsewhere (5). The sampling 0013-936X/86/0920-1257$01.50/0
Table I. Impactor Sampling Periods (Local Time) sample
start
end
2 3
May 7, 4.22 p.m. May 9, 3.22 p.m. May 12, 10.00 a.m.
May 9, 3.28 p.m. May 12, 9.47 a.m. May 14, 11.10 a.m.
4
site was the roof of the Finnish Meteorological Institute building (about 25 m above ground level) in downtown Helsinki. Analysis. The mass of collected particles was determined by weighing substrate films carefully before and after sampling with a microbalance (Mettler M3). Before gravimetric analysis, the films were exposed to an ion stream generated by a polonium a-active source, in order to reduce the effects of electrical charge on the weighing results. Before radioactivity analysis, the films (donut shaped, in the middle of which are the particle deposition spots) were cut into four equal pieces and laid above each other, in order to achieve better y-countinggeometry. As a result, the samples could be approximated with disket geometry. The amount of radioactive isotopes in the sample was determined by measuring its y-spectrum with a cylindrical Ge(Li) detector. The crystal of the detector is drifted coaxially with one end open, and the active volume is about 130 cm3,corresponding to 30% relative efficiency at 1332 keV. The sample was placed on the end cap of the detector. Measurements were performed in a background shield of 12 cm of lead gradually lined with cadmium (1 mm) and copper (0.5 mm) (6). During the measurement, the crystal was ventilated with aged pressurized air to reduce the iodine background. Measuring times were 45 min for the substrate film of each impactor stage of samples 2 and 3 and 100 min for the films of sample 4, respectively. The measured spectra
0 1986 American Chemical Society
Environ. Sci. Technol., Voi. 20, No. 12, 1986
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Table 11. Aerodynamic Cut Diameters of the Impactor with the Measured Mass and Activity Concentrations on Each of the Impactor Stages AA, mBq/m3
D50,ae,
sample
stage
2
1
2 3
4 5 6 7 8 9 10 11
3
1
2 3 4 5 6 7 8 9 10 11
4
1
2 3 4 5 6 7 8 9 10 11
!.ma
0.028 0.052 0.077 0.14 0.29 0.48 1.0 2.0 4.0 8.0 16 0.028 0.052 0.077 0.14 0.29 0.48 1.0 2.0 4.0 8.0 16 0.028 0.052 0.077 0.14 0.29 0.48 1.0 2.0 4.0 8.0 16
Am, r g / m 3
Io3Ru
0.3 0.5 1.9 4.6 6.8 7.0 2.9 7.3 11.6 14.1 10.6 0.2 0.2 1.3 3.4 4.6 5.6 2.4 3.0 3.3 1.4 7.6 0.2 0.4 1.4 3.7 6.1 9.0 5.1 4.3 4.0 3.5 3.2
NDb ND ND ND 2.5 5.5 5.0 ND ND ND ND ND ND ND 3.2 11.5 15.5 7.0 1.5 ND ND 7.2 ND ND ND ND 2.7 6.0 2.5 ND ND ND ND
1311
2.4 3.0 9.6 25.9 27.9 17.6 4.4 ND 3.5 ND ND ND ND 4.0 9.5 8.3 8.9 3.1 1.9 ND ND 3.0 ND ND ND ND 4.4 5.2 2.7 ND ND ND ND
132Te
l37CS
ND ND ND ND ND 7.1 5.0 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
ND ND ND ND ND 4.6 ND ND ND ND ND ND ND ND ND 3.2 3.2 1.7 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
The aerodynamic diameter at the upstream stagnation oressure of the imDactor stage. *Not detected.
HELSINKI 1986 7.5.1622-9.5.15'8
125
HELSINKI 1986
-
7.5.1622 9.5.1SZ2
100 FITTED
75
-7r'
50
25 ni
Figure 1. Measured (histogram) and fitted (curve) mass size distributions of sample 2. A maximum particle size of 100 p m is assumed when plotting the histogram.
were analyzed with the computer program GAMMA-83, which calculates the concentrations of the nuclides in the sample (7). The efficiency calibration of the disket geometry with sample height of 0 mm above the crystal was used in calculating the activities. The results of 1311were calculated from the peak a t 364.5 keV. The measured mass and activity concentrations on each of the impactor stages are shown in Table 11. Data Reduction. Aerosol size distributions were determined from analysis results by assuming the collection efficiency of each impactor stage to be a step function at the cut-point particle size; i.e., no cross-sensitivity corrections were made. The cut points of incompressible flow stages were calculated by Marple's theory (8). The cut points of high-velocity compressible flow stages were de1258
Environ. Sci. Technol., Vol. 20, No. 12, 1986
OD1
01
1
10
Dpae (prn)100
Flgure 2. Example of measured (histogram) and fitted (curve) I3'I size distributions.
termined by assuming a constant Stk,, value, calculating the jet core velocity from the pressure drop across the stage, and evaluating the Cunningham slip correction factor at the upstream stagnation pressure of the impactor stage (3,9,10). The calculated cut points are shown in Table 11. To determine the structure of the size distributions, a log normal distribution was fitted to each measured size distribution with the DISFITE fitting program (11).
Results Examples of measured mass and 1311 differential size distributions (histograms)and their log normal fits (curves) are shown in Figures 1 and 2. Distribution functions above 4 pm a.e.d. are estimates, due to decreasing aspi-
Table 111. Geometric Mean Diameters (Aerodynamic) DG,, Geometric Standard Deviations SG, a n d Modal Concentrations C for Radioactivity Size Distributions and for Mass and Surface Area Size Distributions of t h e Accumulation Mode sample 2
SG
DGae,pm 0.42 0.32 0.83 0.33 0.93
mass surface area lo3Ru 1311
132Te l37CS
sample 3 C,mBq/m3 20“ 321b 14 98 13
1,7 1,7 1.8
1.7 -1.5
sample 4
DGae,pm 0.44 0.31 0.63 0.36
SG 1.8 1.8 1.9 2.3
C,mBq/m3 15“ 251b 46 39
0.63
1.8
9
DGae,pm 0.57 0.38 0.65 0.57
SG 1.9 1.9 1.7 2.0
C,mBq/m3 25” 318b 12
17
Accumulation mode mass concentration, pg/m3. Accumulation mode surface area concentration, pm2/cm3. 1311 size distributions differ clearly from size distributions of other radioactive isotopes. The geometric mean size of 1311is smaller than that of other isotopes. In samples 2 and 3, it is almost equal to the surface area geometric mean diameter of the accumulation mode, and in sample 4 it is equal to the mass geometric mean diameter of the accumulation mode. The geometric mean size of 1311 seems to grow whereas the geometric mean size of lo3Rudecreases, as the aerosol ages. In sample 3, l3II and lo3Ruare also found in particles of D,,> 16 pm (not shown in Figure 4). This is probably due to rainy weather which occurred during the sampling period, Le., radioactivity carried by the raindrops.
Flgure 3. Mass size distribution curves. Sampling periods are given in Table I.
l? 1M)
0.01
Qd
1.0
10
Dp.
Ipml
1W
Flgure 4. Radioactivity size distribution curves of Helsinki atmospheric aerosols.
ration efficiency of the inlet and increasing impactor wall losses in this size range. Mass size distribution curves of samples 2-4 are shown in Figure 3. They are clearly bimodal, exhibiting accumulation and coarse-particle modes and a gap between these at a size range of 1-2 pm a.e.d. Radioactivity size distribution curves of those isotopes, which could be determined with relatively short y-counting times, are shown in Figure 4. All distributions are unimodal. The modal parameters [geometricmean diameter (aerodynamic), geometric standard deviation, and modal concentration] for the accumulation-mode mass and surface area (calculated from mass distribution assuming unit density spherical particles) size distributions and for radioactivity size distributions are given in Table 111.
Registry No. lo3Ru, 13968-53-1; 132Te, 14234-28-7; 137Cs, 10045-97-3; 1311, 10043-66-0.
Literature Cited Berner, A,; Lurzer, C. J. Phys. Chem. 1980,84,2079-2083. Berner, A. In Aerosols. Science,Technology, and Industrial Applications of Airborne Particles;Liu, B. Y. H.; Pui, D. Y. H.; Fissan, H. J., Eds.; Elsevier: New York, 1984; pp 139-142. Kauppinen, E.; Hillamo, R.; Ruuskanen, J.; Hakkarainen, T.; Rouhiainen, P. J. Aerosol Sei. 1986, 17, 506-510. Lui, B. Y. H.; Pui, D. Y. H. Atmos. Enuiron. 1981, 15, 589-600. Savolainen, A.-L.; Hopeakoski, T.; Kilpinen, J.; Kukkonen, P.; Kulmala, A.; Valkama, I. “Dispersion of Radioactive Releases Following the Chernobyl Nuclear Power Plant Accident. Interim Report”; Finnish Meteorological Institute Report No. 1986:2, 1986; Finnish Meteorological Institute, Helsinki. Sinkko, K.; Aaltonen, H. “Calculation of the True Coincidence Summing Correction for Different Sample Geometries in Gamma-Ray Spectroscopy”; Report STUK-BVAL0 40,1985; Finnish Centre for Radiation and Nuclear Safety, Helsinki. Sinkko, K. “Computer Analysis of Gamma-Ray Spectra in Sample Measurements” (in Finnish); Licentiate Thesis, Department of Physics, University of Helsinki, Helsinki, 1981. Rader, D. J.; Marple, V. A. Aerosol Sei. Technol. 1985,4, 141-15. Flagan, R. C. J . Colloid Interface Sci. 1982,87, 291-299. Biswas, P.; Flagan, R. C. Environ. Sci. Technol. 1984,18, 611-616. Whitby, K. T.; Whitby, E. R. “DISFITE-Size Distribution and Fitting Program”; P T L Publication No. 441, 1982; Particle Technology Laboratory, University of Minnesota, Minneapolis, MN.
Received for reuiew June 27,1986. Accepted August 25, 1986.
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