Daily and hourly chemical impact of springtime transboundary aerosols on Japanese air quality

Abstract

Abstract. The regular eastward drift of transboundary aerosol intrusions from the Asian mainland into the NW Pacific region has a~pervasive impact on air quality in Japan, especially during springtime. Analysis of 24-h filter samples (ICP-AES and ICP-MS) and hourly Streaker (PIXE) samples of particulate matter collected continuously for six weeks reveal the chemistry of successive waves of natural mineral desert dust ("Kosa") and metalliferous sulphatic pollutants arriving in Western Japan during spring 2011. The main aerosol sources recognised by PMF analysis of Streaker data are mineral dust and fresh sea salt (both mostly in the coarser fraction PM2.5–10), As-bearing sulphatic aerosol (PM0.1–2.5), metalliferous sodic PM interpreted as aged, industrially contaminated marine aerosol, and ZnCu-bearing aerosols. Whereas mineral dust arrivals are typically highly transient, peaking over a few hours, sulphatic intrusions build up and decline more slowly, and are accompanied by notable rises in ambient concentrations of metallic trace elements such as Pb, As, Zn, Sn and Cd. The magnitude of the loss in regional air quality due to the spread and persistence of pollution from mainland Asia is especially clear when cleansing oceanic air advects westward across Japan, removing the continental influence and reducing concentrations of the more undesirable metalliferous pollutants by over 90%. Our new chemical database, especially the Streaker data, demonstrates the rapidly changing complexity of ambient air inhaled during these transboundary events, and implicates Chinese coal combustion as the main source of the anthropogenic aerosol component.