THE COMPARISON OF RADIONUCLIDES 222Rn AND 210Pb
CONCENTRATIONS IN THE ATMOSPHERE OF
BRATISLAVA
J. Merešová, K. Holý, I. Sýkora, M. Chudý
Department of Nuclear Physics and Biophysics, Comenius University,
Mlynská dolina F1, 842 48 Bratislava, Slovakia
Introduction
The dominant part of the atmospheric radioactivity consists on
222
222
Rn and its progeny.
Rn is the most important radioactive gas present in the lower atmosphere. Its importance
rests on radiohygienic point of view, because
222
Rn and its products are the second most
relevant cause of cancer diseases of respiration tract and lungs after smoking. 222Rn originates
from the decay chain of
238
U and enters into lower atmosphere by emanating and exhaling
from soil. Air activity concentration of 222Rn shows seasonal variations with maximum values
in winter and minimum in summer. It also shows diurnal variations with the maximum in the
night hours and the minimum in the afternoon [1, 2].
The last one of four short-living radon progeny
214
Po decays into
210
Pb. It is
transported through the atmosphere bound to aerosol particles and precipitated back to Earth
by dry or wet deposition. The value of volume activity of
210
Pb is influenced by several
meteorological factors. There are also other possible sources of 210Pb like traffic or industrial
activity.
The aim of this paper is to show the results of the in the long-term measurement of
radioactivity concentration in low level atmosphere [3, 4, 5]. In particular it is concerned with
222
Rn and 210Pb, compared with basic meteorological parameters.
Experimental
Concentrations of
222
Rn in lower atmosphere have been measured by the continual
method using the scintillation chamber. Values have been obtained every half-hour and
averaged for two-hour interval [3].
The
210
Pb concentrations in the atmosphere have been evaluated using nitro-cellulose
filters with hole diameter 0.8 m. After exposing in a sampler device the filters have been
measured by a semiconductor HPGe detector placed in the low-background shield [4, 5].
Results and Discussion
Measured concentrations of
222
Rn and
210
Pb over the period from March 2001 to
December 2003 are presented in figure 1. During this term 73 sets of nitro-cellulose filters
222
were sampled. The concentrations of
Rn ranged from 1.67 to 14.81 Bq.m-3 with a mean
value 5.18  0.11 Bq.m-3. The concentrations of 210Pb ranged from 0.27 to 3.07 mBq.m-3 with
a mean value 0.89  0.02 mBq.m-3.
16,0
3,5
222Rn
14,0
3,0
210Pb
12,0
-3
Pb [mBq.m ]
10,0
2,0
8,0
1,5
210
222
-3
Rn [Bq.m ]
2,5
6,0
1,0
4,0
0,5
2,0
3
1.
0
3
17
.1
3.
0
3
30
.0
2.
0
2
10
.0
1.
0
2
17
.1
6.
0
2
09
.0
4.
0
2
10
.0
1.
0
2
31
.0
1.
0
1.
0
1
09
.0
1
10
.1
9.
0
1
14
.0
7.
0
6.
0
1
24
.0
1
18
.0
5.
0
26
.0
3.
0
4.
0
22
.0
27
.0
1
0,0
1
0,0
Fig. 1 Air activity concentrations of 222Rn and 210Pb in the atmosphere
Both radionuclides show a seasonal variation with higher values of concentration in
autumn to winter period and lower values in spring to summer period. The increase of
concentration in cold season is attributed to frequent inversion conditions of the surface air
layer. The decrease in warm season is a result of intensive air mixing during these months.
Correlation coefficient was found to be equal 0.82 (two points were excluded) (Fig. 2)
what implies a strong correlation between air concentrations of 222Rn and 210Pb. Using aerosol
size distribution the residence time for
210
Pb was estimated 3 – 4 days in summer and 6 – 7
days in winter [6]. We have compared the measured concentration of
210
Pb and the one
calculated from 222Rn concentrations. Assumed that only the measured concentration of 222Rn
is the only one source of 210Pb, the measured level of 210Pb is reached via decay series after 2
– 4 days. From this it follows that the accumulation of 210Pb in the atmosphere does not occur
and aerosols are being deposited on the Earth surface within few days.
2,5
Correlation coefficient
Number of points
0.82
71
y = 0,2253x - 0,2962
R2 = 0,669
210
-3
Pb [mBq.m ]
2,0
1,5
1,0
0,5
0,0
1
3
2
4
5
6
222
-3
7
8
9
10
Rn [Bq.m ]
Fig. 2 Correlation between air activity of 222Rn and 210Pb
The correlation between air concentrations of radionuclides and meteorological
parameters is presented in table 1. The values of correlation coefficients are comparable for
both the radionuclides. Relatively strong correlation between concentrations of both
radionuclides and air pressure is observable. This result is astonishing since between the
radon progeny and the atmospheric pressure the opposite trend was observed [7]. Also
relatively strong influence of air temperature and air humidity is apparent. The increasing air
temperature induced stronger air mixing what effects a remarkable decrease of
222
Rn. The air
humidity is anti-correlated with air temperature therefore there is the correlation with the
concentration of the radionuclides.
Table 1
Correlation coefficients between air concentrations of radionuclides and meteorological
parameters
Air temperature
Air pressure
Air humidity
Precipitation
222
222
Rn*
-0.41
0.24
0.49
-0.18
Rn**
-0.38
0.45
0.34
-0.23
0.30
-0.35
210
Pb
-0.44
0.47
* Month means
** Means during the sampling of atmospheric aerosols
Conclusion
Air activity concentration of gaseous
222
210
Rn and
Pb bound to aerosol particles was
measured. Temporal variation with seasonal behaviour was observed of both radionuclides
and high correlation between this radionuclides (R = 0.82) was found. The concentrations of
222
Rn and
Pb ranged from 1.67 to 14.81 Bq.m-3 with a mean value 5.18  0.11 Bq.m-3 and
210
from 0.27 to 3.07 mBq.m-3 with a mean value 0.89  0.02 mBq.m-3, respectively. These are
typical values of air activity concentrations of
222
Rn and
210
Comparing the calculated and measured concentration of
conclusion that the accumulation of
210
Pb for European area [6, 8].
210
Pb we have come to the
Pb in atmosphere does not occur. Provided that the
measured concentration of 222Rn is the only source of 210Pb the measured level of 210Pb would
be reached via decay series after 2 – 4 days.
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