Transport of anthropogenic aerosols from Asia and subsequent chemical transformation

Aerosol chemical composition and gaseous species were measured at Cape Hedo, Okinawa, Japan (CHO), during the ABC/EAREX project period in March 2005, using high‐time‐resolution instruments including an Aerodyne quadrupole aerosol mass spectrometer (Q‐AMS), a tapered element oscillating microbalance (TEOM), and gas monitors in order to investigate the transport and subsequent chemical transformation of aerosol in the east Asian region. Sulfate was the dominant species in fine aerosol mode and the average concentration of ammonium, sulfate and organics was 1.25, 6.37 and 2.16 μg m−3, respectively. The sulfate concentration observed at CHO in 2005 was about 1.5–2 times higher than that in 1994. For the majority of high‐sulfate observations, the air mass was transported from the central east Chinese region (between Shanghai and the Shandong Peninsula). Sulfate transport was intermittent and strongly correlated with the passage of synoptic‐scale high‐/low‐pressure systems. Chemical components and their concentration showed significant change on 17–18 March, which is accounted for by the change in air mass origin and the synoptic‐scale weather system. In addition, it is suggested that the difference of air quality at the air mass origin reflects the chemical composition at CHO. The high sulfate concentration required heterogeneous conversion of SO2 to sulfate at a rate of 2.0% h−1. A pronounced signal at m/z = 44 confirmed that organic compounds were oxidized.