Lead-210 and Beryllium-7 in the Aerosol Particles Around Taiwan Off-Shore Areas
Titel:
Lead-210 and Beryllium-7 in the Aerosol Particles Around Taiwan Off-Shore Areas
Auteur:
Chung, Yu-Chia Chen, Ping
Verschenen in:
Chemistry & ecology
Paginering:
Jaargang 15 (1998) nr. 1-3 pagina's 167-183
Jaar:
1998-12-01
Inhoud:
Distributions of 210Pb and 7Be in the aerosol particles of different size fractions were measured around Taiwan offshore areas from October, 1994 to October, 1995. the size distribution and abundance of the aerosol particles showed both spatial and temporal variations. the particle concentrations off northwestern Taiwan were more than twice as those off northeastern Taiwan both in November and March, and the values were much higher in November than in March for both areas. the measured particle concentrations, except for one sample with an unusually high value, ranged from 10 to 83 μOgm -3 in the study areas. the 210Pb concentrations in the aerosol particles filtered from the air mass varied between 20 × 10-3 and 72 × 10-3 dpm m-3 (1dpm = 0.45 pCi). the 210Pb concentrations in the area off southwestern Taiwan appeared somewhat higher than in other areas and were probably contributed by the land air from Taiwan which contains higher 210Pb in winter. the 210Pb concentrations off northern Taiwan were low in November when the aerosol concentrations were high, but they were high in March when the aerosol concentrations were low. Based on the 7Be monitoring records of 20 years on the aerosol particles of the island by the Taiwan Radiation Monitoring Center, the mean settling rate averaged 0.91, 0.79 and 0.68 cm s-1, respectively, in northern, central and southern Taiwan. with these values and the 210Pb concentrations in the aerosols, the 210Pb flux was determined to be between 0.58 and 2.30 dpm cm-2y-1, with an average of 1.19 dpm cm-2y-1. Excluding the highest value due to its extremely high 210Pb and aerosol concentrations, the average is reduced to 1.05 dpm cm-2y-1. the activity median diameters (AMD) for 210Pb in the study areas were between 0.69 and < 0.49 μM with a mean of 0.5 om based on 210Pb distributions in different particle size fractions. Thus, 210Pb was preferentially adsorbed on to the submicron particles. 7Be in the study areas showed a good correlation with 210Pb in total activity although the two nucides had different sources.
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