11:00 AM - 11:15 AM
[HTT21-02] Estimation of air pollutant sources from the seasonal variation of Sr and Pb isotope ratios of aerosols
Keywords:aerosol, Sr-Pb isotopes, transboundary air pollution
[Samples and analytical procedure] The sampling site is NOTO Ground-based Research Observatory (NOTOGRO) at the tip of Noto peninsula (37°45’N, 137°36’E). All of the samples were collected weekly on the roof of a building (15 m a.g.l.) using a High-volume air sampler (AH-600F, SHIBATA) with a constant flow rate of 700 L/min. Only the coarse fraction exceeding 2.5 µm in diameter was collected on a 12.6 × 16.6 cm2 SiO2 filter through an impactor. Filters were extracted with 5% HOAc (acetic acid) solution. Residual fraction after extraction with HOAc was digested in HF-HCl-HNO3 solution. Isotopic ratios of Sr and Pb were measured using a Thermo Scientific Triton thermal ionization mass spectrometer (TIMS) and Thermo Scientific Neptune multicollector-inductively coupled plasma-mass spectrometer (MC-ICP-MS), respectively.
[Results and discussion] The HOAc-leachate materials are characterized by low 87Sr/86Sr ratios and approach to a marine value of 0.70918, indicating the dominant contribution of sea salt aerosol. In contrast, the HOAc-residue materials have high 87Sr/86Sr ratios, and sample collected from 9 to 16 July show the highest 87Sr/86Sr ratios similar to surface soil silicates in the north China (0.71432 in average; Nakano et al., 2004). This result supports a view that the continental air-mass may reach to Japan even in summer season. About Pb isotope ratios of the HOAc-leachate materials, samples with low V/Mn showed similar Pb isotopic ratios reported in China. Major sources of V and Mn are from oil combustion and coal combustion, respectively. This result suggests that the air-mass over NOTOGRO in spring to early summer of 2015 are affected by the coal-derived aerosols in China.