Compound-specific radiocarbon analysis of individual fatty acids was conducted for a semi-urban aerosol sample using preparative capillary gas chromatography (PCGC) system and accelerator mass spectrometry (AMS). The aerosol fatty acids (C16 to C34) showed a typical bimodal distribution with two maxima at C16 and C26. Their carbon isotopic compositions ranged from -30.3 ? (C26) to -23.3 ? (C18), suggesting that they are derived from terrestrial higher plants and marine sources. Radiocarbon measurements of C16-C22 fatty acids showed modern 14C ages, suggesting that the acids are emitted from living higher plants and possibly from marine organisms. On the other hand, C24-C26 fatty acids that are characteristic to terrestrial plant waxes showed 14C ages of 5860 (¿200) years. This suggests that some portion of higher molecular weight fatty acids have been stored in geochemical reservoirs such as soils at least for hundreds to thousands of years and then emitted to the atmosphere. These aged fatty acids could be in part transported long distances from the Asian continent through the atmosphere. ¿ 2001 American Geophysical Union