Long-term variability of inorganic ions in TSP at a remote background site in Japan (Wajima) from 2005 to 2015

Eleven years (2005-2015) of data from long-term monitoring at a Japanese remote background site in Wajima, were analyzed to investigate temporal trends and sources. Water-soluble inorganic ions (WSIIs) were analyzed for aerosol chemical composition. The total WSIIs concentration was 7.93 ± 3.93 μg/m³, accounting for 42.3% of TSP mass, ranged from 11.4 to 93.9%. SO₄^2- is the most abundant ion, contributing a total WSII mass from 18.0 to 79.8%, and non-sea-salt (nss-) SO₄^2- contributed from 63.6% to 99.6% of total SO₄^2-, which was related to human activities on the Asian continent and the effects of marine precursors in spring and summer, respectively. NO₃^- and NH₄⁺ contribute 6.3 and 7.4% of the total WSIIs and were affected by long-range transport and local sources as well. The increasing trend of Na⁺ and Cl^- indicates the increased influence of sea salt, which is caused by more frequent strong winds. K⁺ is mainly produced from biomass burning with a stable seasonal variation, Ca²⁺ as the characteristic ion of dust has the highest concentration in spring. Mg²⁺ comes from minerals and marine sources during spring and summer, respectively. This work describes in detail the annual change trend of the WSIIs of atmospheric particles in the Wajima area, seasonal characteristics, and source contributions, provide a comprehensive understanding of long-term variation in atmospheric particulate.