HR: 0830h
AN: A21E-1022    [PDF]
TI: Distribution of $^{7}$Be, $^{210}$Pb and $^{210}$Po in Size Fractionated Aerosols From Northern Taiwan
AU: * Su, C
EM: ccsu@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei, 115 Taiwan
AU: Huh, C
EM: huh@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei, 115 Taiwan
AB: The partition of $^{7}$Be, $^{210}$Pb and $^{210}$Po in size fractionated aerosols was studied using samples collected from Nankang (northern Taiwan) during July 2002-July 2003. A TSP air sampler coupled to a 6-stage cascade impactor was used to collect large-volume samples and separate the aerosols into six size classes with the cut-off points at 7.2 $\mu$m, 3 $\mu$m, 1.5 $\mu$m, 0.95 $\mu$m and 0.49 $\mu$m. The total mass concentrations of the aerosol samples ranged from 23 to 99 $\mu$g m$^{-3}$, with a maximum (18-50 %) falling at the sixth stage ($<$ 0.49 $\mu$m) and a minimum (5-13 %) at the third stage (1.5-3.0 $\mu$m). Total concentrations of $^{7}$Be, $^{210}$Pb and $^{210}$Po in the samples were 0.11-0.56, 0.012-0.100 and 0.0009-0.0158 dpm m$^{-3}$, respectively. For most of the samples, more than 70 % of the radioactivities are found in the fifth and sixth stages ($<$ 0.95 $\mu$m). Concurrent with the measurements of $^{7}$Be and $^{210}$Pb concentrations in aerosols, we have also measured the fluxes of these nuclides. Coupling the concentration data with the flux data, we obtained an overall deposition velocity of 0.02-3.71 cm s$^{-1}$ for $^{7}$Be and 0.09-6.18 cm s$^{-1}$ for $^{210}$Pb, without any obvious seasonal variation during the experimental periods. The size of aerosol particles and the height of cloud are the major factors controlling the deposition velocity of $^{7}$Be and $^{210}$Pb. The time series of $^{210}$Po/$^{210}$Pb was in phase with that of $^{7}$Be/$^{210}$Pb and showed an increase during the spring and summer, probably reflecting stratospheric folding in the spring and more vigorous tropospheric mixing (e.g., due to typhoons) in the summer.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 1040 Isotopic composition/chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting