Long-term characterization of major water-soluble inorganic ions in PM10 in coastal site on the Japan Sea

PM₁₀ samples were collected over three years at Monzenmachi, the Japan Sea coast, the Noto Peninsula, Ishikawa, Japan from January 17, 2001 to December 18, 2003, using a high volume air sampler with quartz filters. The concentrations of the water-soluble inorganic ions in PM₁₀ were determined with using ion chromatography. By analyzing the characteristics of these, the evidences were found that the Asian outflow had an obviously influence on the air quality at our study site. The results were as follows: the secondary pollutants SO₄²⁻, NO₃⁻ and NH₄⁺ were the primary water-soluble inorganic ions at our study site. The monthly mean concentrations of SO₄²⁻, NH₄⁺, NO₃⁻ and Ca²⁺ have prominent peak in spring due to the strong influence of the Asian continent outflow—these according to backward air trajectory analysis, the maximum of which were 6.09 for nss-SO₄²⁻ in May, 2.87 for NO₃⁻ and 0.68 μg m⁻³ for nss-Ca²⁺ in April, respectively. Comparable to similar data reported from various points around East Asia, it had the characteristics of a polluted coastal area at our study site. The concentration of nss-Ca²⁺ in PM₁₀ drastically increased when the Asian dust invaded, the mean value during the Asian dust days(AD) was 0.86 μg m⁻³, about 4 times higher than those of normal days (NAD). Meanwhile, the mean concentrations of nss-SO₄²⁻, NO₃⁻ and NH₄⁺ in AD periods were higher than those in NAD periods which were 5.87, 1.76 and 1.82 μg m⁻³, respectively, it is due to the interaction between dust and secondary particles during the long-range transport of dust storms. Finally, according to the source apportionment with positive matrix factorization (PMF) method in this study, the major source profiles of PM₁₀ at our study site were categorized as (1) marine salt, (2) secondary sulfate, (3) secondary nitrate and (4) crustal source.