Long-term observation of trace metal concentration in aerosols at a remote island, Rishiri, Japan by using inductively coupled plasma mass spectrometry equipped with laser ablation

Aerosol samples were continuously collected at Rishiri Island, Japan and concentrations of trace metals and water-soluble ionic constituents in the aerosol samples were measured in this study. Trace metal concentrations were analyzed by using inductively coupled plasma mass spectrometry equipped with a laser ablation sample introduction (LA/ICP-MS), which is a rapid and simultaneous method for multi-element analysis. The average concentrations of trace metals and water-soluble ionic constituents in TSP at Rishiri Island from March 2001 to October 2003 were: Al: 251 ± 371 (n= 359), Ti: 27 ± 38 (n= 342), V: 1.3 ± 1.6 (n= 327), Cr: 2.0 ± 2.2 (n= 202), Mn: 8.6 ± 12.0 (n= 353), Fe: 356 ± 645 (n= 349), Co: 0.18 ± 0.25 (n= 250), Ni: 1.9 ± 3.4 (n= 232), Cu: 7.4 ± 10.2 (n= 123), Zn: 16 ± 20 (n= 242), As: 1.2 ± 2.1 (n= 312), Se: 0.49 ± 0.65 (n= 133), Cd: 0.19 ± 0.33 (n= 285), Sb: 0.46 ± 0.62 (n= 265), Pb: 16 ± 30 (n= 314), Na⁺: 1153 ± 1384 (n= 306), NH₄ ⁺: 247 ± 257 (n= 254), K⁺: 74 ± 63 (n= 284), Ca²⁺: 144 ± 174 (n= 294), Mg ²⁺: 150 ± 161 (n= 293), Cl^-: 2703 ± 3151 (n= 180), NO₃ ^-: 339 ± 415 (n= 332), SO₄ ^2-: 1648 ± 1398 (n= 362) (unit: ng m^-3). The obtained trace metal concentration levels in the aerosol were 1/10-1/70 of those obtained at Beijing, China and 1/2-1/40 of those obtained at Tokyo, Japan. The correlation between Al, Ti, Mn, and Fe, which were derived mainly from soil dust, was high at Rishiri Island. High-concentration events (when the measured value exceeds the average +3σ for the entire observation period) for each chemical constituent were observed several times per year, although the chemical concentration levels in TSP at Rishiri Island were almost constant throughout the year. The high-concentration phenomenon, which occurred in only 2% of the measurement days, raised the average concentration of the atmospheric chemical constituents at Rishiri Island by about 10%. The average value of the Pb/Zn ratio at Rishiri Island during the entire period was 1.8 ± 2.9, which is higher than 1. This suggests that the atmosphere at Rishiri Island has constantly been receiving contaminants from the Asian Continent. We conclude that the chemical constituents in the aerosol at Rishiri Island have been regularly transported from a wide area across the Asian Continent.