ABSTRACT

Stable carbon (δ¹³C) and hydrogen (δD) isotopic compositions of n-alkanes in total suspended particles from Tokyo were measured to decipher their source and transport in the polluted urban atmosphere. The δ¹³C and δD values of the C₂₁ to C₃₃ n-alkanes ranged from -25.5 to -32.8‰ and -55 to -157‰, respectively. The δ¹³C values are within the range of those in terrestrial higher plants and fossil fuel. In contrast, the δD values of the C₂₁ to C₂₄ n-alkanes and the C₂₆ to C₃₂ even-carbon numbered n-alkanes are in the range of those typical to marine crude oil, indicating that these n-alkanes are primarily derived from the anthropogenic emission of petroleum hydrocarbons. Lower δD values were found in the C₂₅ to C₃₃ odd-carbon numbered n-alkanes than other homologues, suggesting that the long chain n-alkanes are significantly contributed from terrestrial higher plant waxes in addition to fossil fuel hydrocarbons. The δD values of the C₂₉ and C₃₁ n-alkanes show a strong negative correlation with CPI (carbon preference index), which enable us to eliminate fossil fuel contribution using a mass balance approach. Large seasonal variations in the δD values corrected for fossil fuel contribution and their relation to seasonal differences in air mass transport suggest that terrestrial higher plant-derived n-alkanes in the Tokyo aerosols likely originate from the raw leaves of local vegetation. The corrected δD values based on CPI of 10 are in good agreement with those in contemporary vegetation in Tokyo, indicating that local vegetation is more important as a source of terrestrial higher plant-derived n-alkanes in the polluted urban atmosphere.