Field Studies for Secondary Organic Aerosol in the Transboundary Air

Monday, 15 December 2014
Satoshi Irei1, Akinori Takami2, Yasuhiro Sadanaga3, Susumu Nozoe2, Masahiko Hayashi4, Keiichiro Hara4, Takemitsu Arakaki1, Shiro Hatakeyama5, Takao Miyoshi2, Yoko Yokouchi6 and Hiroshi Bandow3, (1)University of the Ryukyus, Okinawa, Japan, (2)Nat'''l Inst. Environ. Studies, Tsukuba, Ibaraki, Japan, (3)Osaka Prefecture University, Sakai, Japan, (4)Fukuoka University, Fukuoka, Japan, (5)Tokyo University of Agriculture and Technology, Tokyo, Japan, (6)NIES National Institute of Environmental Studies, Ibaraki, Japan
To study formation of secondary organic aerosol (SOA) in the air outflowed from the Chinese continent and its fraction in an urban city located in downwind, we have conducted field studies at two background sites and one urban site in the western Japan: the Cape Hedo Aerosol and Atmospheric Monitoring Station (26.9˚N, 128.3˚E), the Fukue Atmospheric Monitoring Station (32.8˚N, 128.7˚E), and Fukuoka University (33.6˚N, 130.4˚E), respectively. During the studies, stable carbon isotope ratio (δ13C) of low-volatile water-soluble organic carbon (LV-WSOC) was measured in 24 h collected filter samples of total suspended particulate matter. Concentration of fine organic aerosol and the proportion of the signal at m/z 44 (ions from the carboxyl group) in the organic mass spectra (f44) were also measured by Aerodyne aerosol mass spectrometers. Limited to the Fukue site only, mixing ratios of trace gas species, such as aromatic hydrocarbons, NOx, and NOy, were also measured using GC-FID and NOx and NOyanalyzers for estimation of photochemical age (t[OH]).

A case study in December 2010 showed that plots of δ13C versus f44 showed systematic variations at Hedo and Fukue. However, their trends were opposite. At Fukue the trend was consistent in the plot of δ13C of LV-WSOC versus t[OH] estimated by the NOx/NOy or the hydrocarbon ratios, indicating influence of SOA. The systematic trends aforementioned qualitatively agreed with a binary mixture model of SOA with background LV-WSOC having the f44 of ~0.06 and the δ13C of -17‰ or higher, implication of some influence of primary emission associated with C4plants.

Given that the LV-WSOC at the urban Fukuoka site was a binary mixture, a mass balance for δ13C was constructed below. In the equation, δ13CMix, δ13CLocal, δ13CTrans, and FLocal are δ13C of binary LV-WSOC mixture, δ13C of LV-WSOC from local emission origin, δ13C of LV-WSOC from transboundary pollution origin, and a fraction of LV-WSOC from local emission origin in the mixture, respectively. We applied d13C values at Fukuoka and Fukue to δ13CMix and δ13CTrans, respectively, and δ13C of -27‰ for vehicular emission to δ13CLocal. The preliminary results demonstrated that, except some negative FLocal, the majority of calculated FLocal ranged from 4% to 86% and the lower FLocal, the higher LV-WSOC concentration.