Characterization of n-alkanes in PM2.5 of the Taipei aerosol

Ambient concentrations of n-alkanes with carbon number ranging from 17 to 36 were determined for PM2.5 samples collected in Taipei city during September 1997–February 1998. The measured concentrations of particulate n-alkanes were in the range of 69–702 ng m−3, considerably higher than the concentration levels observed in Los Angeles and Hong Kong. The concentration distributions of n-alkanes homologues obtained in this study exhibited peaks at C19, C24 or C25. This suggests that fossil fuel utilization, such as vehicular exhaust and lubricant residues, was an important contributor to the Taipei aerosol. Source apportionment of PM2.5 was conducted using carbon preference index (CPI, defined as the ratio of the total concentration of particulate n-alkanes with odd carbon number to that with even carbon number) and U : R ratio (the concentration ratio of unresolved components to resolved components obtained from chromatograms). The low CPI value (0.9–1.9) and high U : R ratio (2.6–6.4) for each sample further confirmed that fossil fuel utilization was the major source of n-alkanes in ambient PM2.5 of Taipei city. Estimates from these results showed that 69–93% of the n-alkanes in PM2.5 of the Taipei aerosol originated from vehicular exhaust. The higher concentration level of particulate n-alkanes in the Taipei aerosol was mainly a result of vehicular emissions.