Thursday, 8 September 2005

This presentation is part of: Poster Session II

Investigation of source apportionment for carbon component in airborne particulate based on 14C measurements of organic and elemental carbons

Motohiro Hirabayashi1, Ken Shibata2, Atsushi Muramoto2, Jun Yoshinaga2, Shinji Kobayashi3, Minoru Yoneda1, Kiyoshi Tanabe1, Yasuyuki Shibata1, and Motoyuki Matsuo4. (1) Environmental Chemistry Division, National Institute for Environmental Studies, Tsukuba, Japan, (2) Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan, (3) PM2.5 & DEP Research Project, National Institute for Environmental Studies, Tsukuba, Japan, (4) Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan

Airborne particulates are mixture of various substances originated from various sources. One of the major components of airborne particulates is carbon component consists of elemental carbon (EC) and organic carbon (OC). There are anthropogenic and natural sources of airborne carbon component. Most of EC is combustion origin. And most of EC can be considered fossil fuel origin where biomass combustion such as field burning, forest fire, municipal incineration are not dominant sources, i.e., urban areas. OC originates from combustion, evaporation of solvents, volatile organic compounds of plant origin, fine fragments of an organism and so on. The biogenic carbon contains 14C at the almost same ratio to the atmosphere. However, 14C is not contained in the carbon of fossil fuel origin. Therefore, it is possible to estimate the biomass/fossil carbon ratio based on 14C measurement of particulate samples. In this study, in order to provide important information for source apportionment of aerosol pollution, the method for measuring percent modern carbon (pMC) of EC and OC has been developed. Samples were collected besides a road (crossing) with heavy traffic of diesel vehicle in metropolitan area, where fossil fuel origin particles are dominant. Another sampling site was selected in suburban area where many sources of biomass origin expected to contribute. Thermal separation of OC from EC at 800 deg C under He stream was suggested to be suitable for pMC measurement of EC. The pMC value of EC was significantly smaller than that of TC (Total carbon) for the samples at suburban site, which means that contribution of EC of fossil fuel origin is considerably larger in EC compared to TC. On the other hand, the value of pMC of TC of a roadside samples were very small, which support the carbon component at roadside in metropolitan area was mostly fossil fuel origin. By combining the radiocarbon analysis of EC, TC and conventional thermo/optical EC/OC analysis, biomass/fossil ratio of EC and OC has been successfully estimated. The results of the preliminary monitoring of pMC by the developed method will also be presented.

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