Author(s)

WEIQIAN WANG & QINGYUE WANG

Abstract

Metropolitan Tokyo area in Japan suffered from a strong Asian dust event which was lasted for 3 days from May 6 to May 8 in 2017. Asian dust particles are usually originated from the deserts of Mongolia and Kazakhstan and could be absorbed air pollutants contained the metals, water-soluble and organic matters during transport process. In this research, two sampling sites called 10F (30m height above ground level) and roadside in Saitama were selected to collect five different size particles (PM_1.1, PM_1.1–2.0, PM_2.0–3.3, PM_3.3–7.0 and the coarse particles (>7.0 μm) of three different events: (1) before Asian dust event (B.A.), (2) during Asian dust event (D.A.) and (3) after Asian dust event (A.A.). Eight watersoluble ionic and 23 elemental species in D.A. event were higher than other periods. In D.A. event, the
ionic contents in 10F were high to 10.3 μg/m³ and the elemental contents in roadside were 6.50 μg/m³ which were higher than those in roadside. Ionic contents were mainly distributed in PM_1.1 with the high contents of secondary particles (NH₄
⁺, NO₃⁻ and SO₄²⁻). Ca²⁺, Cl⁻ and Na⁺ were more enriched in the coarse particles. Ion balance in D.A. event was more basic in 10F and more acidic in roadside. The higher ratios of NO₃⁻/SO₄²⁻ in PM_1.1 were also occurred in D.A. event. Total elements were high (6,050 ng/m³) in 10F with the several times increasing in PM_3.3–7.0 and the coarse particles, and the great contribution form the crustal elements (Al, Fe, Na, Mg and K). Enrichment factors (EFs) of trace elements in PM_1.1 indicating the anthropogenic sources might be the main sources of those ions. EFs in the coarse particles indicating high concentrations of crustal elements might be affected by the Asian dust event. The analysis of air masses backward trajectories showed that the deserts of Mongolia and Kazakhstan and the northern part of China were the important air pollutant origins in Asian dust events
with long-distance transport.

Keywords

Asian dust, metal elements, Saitama, water-soluble inorganic ions.