| 英文摘要 |
The objectives of this study are to develope analytical methods for determination of isotopes in fine particulate matters (PM2.5) and to feasibility of identifying potential sources of ambient PM2.5 with the isotopic fingerprints. To achieve the objectives, ambient PM2.5 sampling was carried out at the Cap Fuguei (CAFÉ), Taipei (NTU), Yangminshan, Douliu and Chayi stations. Besides, in order to establish isotope fingerprints of specific sources, vehicle-emitted particles were collected in the Hsuehshan Tunnel and coal materias together with fly ash and bottom ash were collected from coal-fire power plants. These samples were analyzed for water soluble ions, elemental carbon, organic carbon and metallic constituents. In addition, carbon along with lead and stronitium isotopes were also determined by cavity ring-down spectrometry (CRDS) and multi-collector inductively plasma mass spectrometer (MC-ICP-MS), respectively. The results showed that organic carbon, which accounted for 15-41% of PM2.5 mass, was the predominant species, followed by non-sea-salt sulfate (14-29%), ammonium (6-13%), nitrate (2-16%) and elemental carbon(2-9%). The elevated abundance of OC in the summertime was attributed to the formation of secondary organic aerosols, whereas lower nitrate concentrations were due to evaporation under high atmospheric temperature. Elevated level of sea salt particles was observed at CAFÉ station located in the coastal area, whereas EC and nitrate were found enriched in PM2.5 samples collected at downtown stations.
Using CRDS and MC-ICP-MS instruments, C, Pb and Sr isotopes in PM2.5 samples were detected with high precision and accuracy. The averaged δ13CTC in PM2.5 at CAFÉ and NTU stations were -26.7 and -27.0‰ during summertime, which were lighter than those in the spring period by 2.5‰. The stable carbon isotope ratio measured in the summertime were representative of the local emissions as Taiwan was isolated from continental air mass. On the contrary, the isotopically heavy carbon aerosols in the springtime were attributed to the influences of PM2.5 from mainland China. This inference was supported by δ13CTC data coupling with WRF/Chem model simulations. The averaged δ13CTC in PM2.5 collected at the Douliu and Chayi stations during autumn/winter season were -28.9 and -28.4‰, respectivevly, suggesting local origins. Similar seasonal patterns were found for 208Pb/207Pb ratio. At CAFÉ and NTU stations, the average values of 208Pb/207Pb ratio in the summertime were 2.4227 and 2.4312, respectively. The ratios increased to 2.4408 and 2.4318 in the spring sampling period, which were very close to those obtained in central and northern China, indicating long-range transport of air pollution by Asian continental outflows. The 208Pb/207Pb ratios at Douliu and Chayi stations in the autumn/winter periods were 2.4286 and 2.4291, respectively, suggesting local sources. For 87Sr/86Sr, the average values at all the stations varied between 0.708628 and 0.721940. Unlike δ13CTC and 208Pb/207Pb, no significant seasonal variation was found in 87Sr/86Sr. In case of vehicle-derived PM2.5, the average δ13CTC was -24.4‰ which was comparable to that (-25.1‰) of coal ash collected from coal-fired power plants. In addition, this study also determined 208Pb/207Pb and 87Sr/86Sr ratios for vehicle-emitted PM2.5 with the average values of 2.4380 and 0.711460, respectively.
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