14C measurement for size-fractionated airborne particulate matters

A methodology to measure 14C/12C of the size-fractionated airborne particulate matter (APM) collected on large quartz substrates in a cascade impactor was established to elucidate the size-fractionated source–receptor relationship of the urban APM in Tokyo. The graphite for the 14C measurement by the accelerator mass spectrometry was successfully produced from the resultant gas when the APM sample was combusted with increased amounts of 5.0 g copper (II) oxide, 2.5 g copper metal and 0.1 g silver foil in a specially designed large volume combustion tube. In our preliminary field investigation, the percent modern carbon (pMC) values of the size-fractionated APM samples ranged from 37.7 to 65.1 and decreased with particle size, indicating the importance of fossil fuel origins for finer particles. Approximately 40 pMC for the APM of d<1.1 μm was, however, appreciably higher than our prior expectation. This indicated biomass carbons also contributed significantly to the fine particles in Tokyo.