10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Transboundary Transport of Anthropogenic Sulfur in PM2.5 at a Coastal Site in the Sea of Japan during 2013 to 2016
YAYOI INOMATA, Kanazawa University
Abstract Number: 707 Working Group: Aerosol Chemistry
Abstract In Japan, which is located downwind of the prevailing winds drawn from the Asian continent, high concentrations of PM2.5 were observed at several locations and times, the values exceeding the target value of environmental standard on daily average in Japan (35 maicrog m-3 per day). The sulfur isotopic ratio (34S/32S) is regarded as useful chemical tracers to investigate the source contributions of sulfate in aerosols and precipitation, because the values are different among the sources (1). In this study, daily observations of 34S/32S in PM2.5 were carried out the Niigata-Maki site facing to the Sea of Japan during the intensive monitoring periods from 2013 to 2016.
Airborne particulate samples were collected at the National Niigata-Maki Acid Deposition Monitoring station (hereafter Niigata-Maki, 138.85°E, 37.81°N), which is located facing to the Sea of Japan. A high volume air sampler with PM2.5 impactor (HVI2.5) was used to sampling. Intensive sampling was performed in four seasons from 2013 to 2016. The airborne particulate samples were collected over a 24 hr period. PM2.5 samples were collected on a quartz fiber filter (2500 QAT-UP, Pall Science Co. Ltd.) after the coarse particles (diameter > 2.5 microm), which were collected on a separate quartz fiber filter (HV-SF, Pall Science Co. Ltd.). The samples were analyzed by stable isotope mass spectrometry (Delta Plus, Thermo Co. Ltd.). Canyon Diablo Troilite (CDT) was used as standard.
The 34S/32Snss in PM2.5 ranged from -0.1 to 6.7‰. It showed a seasonal variation with relatively higher values being observed in winter (2.3-6.7‰) compared with values in the other seasons (1.0-4.2‰ in spring, -0.1-4.5‰ in summer, 1.3-5.8‰ in autumn). These data were classified by using the air mass transport routes: directly transported air mass after leaving the Asian continent (TRB), the air mass transported over the Japanese islands after leaving the Asian continent (including domestic sources; DOM), and the air mass transported over the Pacific Ocean and the Japanese islands in summer (NPO). In 2016 summer, the air mass was transported over the Pacific Ocean before arriving at the Niigata-Maki monitoring station. The 34S/32Snss in this period was 0.86±0.56‰, which are same level to the 34S/32S in oil. Considering that the dominant source of sulfate in Japan is oil combustion, these values suggest the domestic emission is dominant source to sulfate in summer. Furthermore, the PM2.5 mass concentrations were relatively larger in summer compared with those in other season. The 34S/32Snss suggest that the increase of aerosol mass concentrations is due to the mixing and growth by domestic precursor gases. In the air mass transported over the Sea of Japan after leaving the Asian continent and arrived to the Niigata-Maki, the 34S/32Snss values for TRB (3.9±0.1‰) are higher than those for DOM (3.1±1.0‰). The 34S/32Snss values for TRB were often observed in winter and close to the values in aerosol measured in northern China. It is also noted that the 34S/32Snss values in TRB in winter are almost same from 2013 to 2016, although sulfate concentrations were decreased.
The lower 34S/32S nss in the air mass transported over the Japanese islands arriving over the site (DOM) are resulting with mixing of the emissions from the Japanese islands and the transboundary transported SO42- in PM2.5. The relative contribution of transboundary transport component to sulfate in PM2.5 was estimated by using the mass balance model. The relative contribution of transboundary component in TRB was 66±13%. The contribution from transboundary transport was large in winter. It is also noted that the relative contribution from DOM in summer are more than 60 %. These results suggest that PM2.5 emitted from the Asian continent are modified during transboundary transport.
[1] Inomata et. al (2016) Sci. Total. Environ. 553, 617.