Limits...
Cosmogenic (22)Na, (7)Be and terrestrial (137)Cs, (40)K radionuclides in ground level air samples collected weekly in Kraków (Poland) over years 2003-2006.

Błażej S, Mietelski JW - J Radioanal Nucl Chem (2014)

Bottom Line: The results for (40)K and (137)Cs are also presented for reference and comparison.Presented frequency distributions for activity concentration and correlation between the obtained results are discussed.The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides.

View Article: PubMed Central - PubMed

Affiliation: The Henryk Niewodniczański Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Kraków, Poland.

ABSTRACT

A low background gamma spectrometer with an Etruscan, 2500 years old lead shield and a muon veto detector were applied to study (22)Na and (7)Be activity concentration in ground level air aerosol samples collected weekly over the years 2003-2006 in Kraków. Each sample was formed with ca 100 000 m(3) of passed air, collected with two parallel ASS-500 high volume air samplers. The results for (40)K and (137)Cs are also presented for reference and comparison. Presented frequency distributions for activity concentration and correlation between the obtained results are discussed. The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides. Moreover, the seasonal variation in nucleus activity ratio was also noticed for (22)Na and (7)Be. Cosmogenic radionuclides being mainly of stratospheric origin, are subsequently attached to fine aerosols, via which they are transported to the ground level air. The mean aerosol transport time within the troposphere was estimated as equal to 7.5 days on average, reaching even 50 days in warm seasons. Limitations of the applied model were identified.

No MeSH data available.


Aactivity ratio 7Be/22Na (Ra) in ground level air as a function of retention time for aerosols in the stratosphere (Ts). The curves present results of the model given by Eq. 1 [4]. The retention time in the troposphere Tt can be read out from the picture provided Ra is known and Ts assumed
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Fig7: Aactivity ratio 7Be/22Na (Ra) in ground level air as a function of retention time for aerosols in the stratosphere (Ts). The curves present results of the model given by Eq. 1 [4]. The retention time in the troposphere Tt can be read out from the picture provided Ra is known and Ts assumed

Mentions: The results presented here allow to adopt a model for aerosol retention developed by Tokuyama and Igarashi [4]. In the original paper the model was applied as follows: the ratio of activity concentration in ground level air 7Be/22Na (equal to Ra in Eq. 1) was used to estimate the retention time for aerosols in the troposphere, Tt (Eq. 1). Since this ratio is season dependable, it should be calculated for each season separately. Frequency distribution for the 7Be/22Na activity ratio does not take a Gaussian shape, it is rather bimodal or polymodal (see Fig. 6). The data for summer (with high 22Na values, so with relatively smaller uncertainties) display the narrowest distribution. Likely, some of the width observed for the frequency distributions comes from the relatively high uncertainties in 22Na activity concentration. The mean value for all our results (n = 173) is equal to Ra = (15.9 ± 5.1) × 103, whereas seasonal mean values are shown in Table 3 together with similar results for Japan in 1998. In both countries they were lower for spring and summer (close to 1 × 104) and higher (close to 2 × 104) for autumn or winter, however the seasonal difference is bigger for Poland which likely results from the lack of autumn maximum of cosmogenic radionuclides reported for Japan (see “Introduction”). Taking into consideration the mean or median value for Ra and assuming retention time in the stratosphere Ts equal to 20 days [4] the resulting mean retention time Tt is equal to about 7.5 days for the entire data set, whereas for warm seasons (when Ra is close to 1 × 104), with the same Ts the value of Tt assumed, it grows to about 50 days (Fig. 7). The cold season with Ra close to 2 × 104 seems to be well described with this model. Ts massively longer then 20 days assumed in the original model [4], namely ranging from 102 to 205 days, was obtained recently within the same model in another study [24]. In the presented paper, the Tt is assumed as known, based on 210Po/210Pb system, and the model was used to determine Ts. With longer Ts applied, much shorter Tt is obtained, far below 10 days as it can be seen from Fig. 7. It does not seem to be very realistic, revealing rather weakness of the applied model.Fig. 6


Cosmogenic (22)Na, (7)Be and terrestrial (137)Cs, (40)K radionuclides in ground level air samples collected weekly in Kraków (Poland) over years 2003-2006.

Błażej S, Mietelski JW - J Radioanal Nucl Chem (2014)

Aactivity ratio 7Be/22Na (Ra) in ground level air as a function of retention time for aerosols in the stratosphere (Ts). The curves present results of the model given by Eq. 1 [4]. The retention time in the troposphere Tt can be read out from the picture provided Ra is known and Ts assumed
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig7: Aactivity ratio 7Be/22Na (Ra) in ground level air as a function of retention time for aerosols in the stratosphere (Ts). The curves present results of the model given by Eq. 1 [4]. The retention time in the troposphere Tt can be read out from the picture provided Ra is known and Ts assumed
Mentions: The results presented here allow to adopt a model for aerosol retention developed by Tokuyama and Igarashi [4]. In the original paper the model was applied as follows: the ratio of activity concentration in ground level air 7Be/22Na (equal to Ra in Eq. 1) was used to estimate the retention time for aerosols in the troposphere, Tt (Eq. 1). Since this ratio is season dependable, it should be calculated for each season separately. Frequency distribution for the 7Be/22Na activity ratio does not take a Gaussian shape, it is rather bimodal or polymodal (see Fig. 6). The data for summer (with high 22Na values, so with relatively smaller uncertainties) display the narrowest distribution. Likely, some of the width observed for the frequency distributions comes from the relatively high uncertainties in 22Na activity concentration. The mean value for all our results (n = 173) is equal to Ra = (15.9 ± 5.1) × 103, whereas seasonal mean values are shown in Table 3 together with similar results for Japan in 1998. In both countries they were lower for spring and summer (close to 1 × 104) and higher (close to 2 × 104) for autumn or winter, however the seasonal difference is bigger for Poland which likely results from the lack of autumn maximum of cosmogenic radionuclides reported for Japan (see “Introduction”). Taking into consideration the mean or median value for Ra and assuming retention time in the stratosphere Ts equal to 20 days [4] the resulting mean retention time Tt is equal to about 7.5 days for the entire data set, whereas for warm seasons (when Ra is close to 1 × 104), with the same Ts the value of Tt assumed, it grows to about 50 days (Fig. 7). The cold season with Ra close to 2 × 104 seems to be well described with this model. Ts massively longer then 20 days assumed in the original model [4], namely ranging from 102 to 205 days, was obtained recently within the same model in another study [24]. In the presented paper, the Tt is assumed as known, based on 210Po/210Pb system, and the model was used to determine Ts. With longer Ts applied, much shorter Tt is obtained, far below 10 days as it can be seen from Fig. 7. It does not seem to be very realistic, revealing rather weakness of the applied model.Fig. 6

Bottom Line: The results for (40)K and (137)Cs are also presented for reference and comparison.Presented frequency distributions for activity concentration and correlation between the obtained results are discussed.The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides.

View Article: PubMed Central - PubMed

Affiliation: The Henryk Niewodniczański Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Kraków, Poland.

ABSTRACT

A low background gamma spectrometer with an Etruscan, 2500 years old lead shield and a muon veto detector were applied to study (22)Na and (7)Be activity concentration in ground level air aerosol samples collected weekly over the years 2003-2006 in Kraków. Each sample was formed with ca 100 000 m(3) of passed air, collected with two parallel ASS-500 high volume air samplers. The results for (40)K and (137)Cs are also presented for reference and comparison. Presented frequency distributions for activity concentration and correlation between the obtained results are discussed. The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides. Moreover, the seasonal variation in nucleus activity ratio was also noticed for (22)Na and (7)Be. Cosmogenic radionuclides being mainly of stratospheric origin, are subsequently attached to fine aerosols, via which they are transported to the ground level air. The mean aerosol transport time within the troposphere was estimated as equal to 7.5 days on average, reaching even 50 days in warm seasons. Limitations of the applied model were identified.

No MeSH data available.