Gas chromatographic screening of organic compounds in urban aerosols: II. Changes in hydrocarbon composition during storage

Abstract

Gas chromatographic and gas chromatographic—mass spectrometric analyses of inadequately stored filters and hydrocarbon extracts of urban aerosols have shown the occurrence of microbially mediated transformation processes giving rise to hydrocarbon patterns different from the original composition of the samples. In all cases, a strong decrease in the concentration of the unresolved complex mixture of hydrocarbons is observed. The modifications also involve the formation of mixtures of C 29–C 34 iso- and anteisoalkanes and modal distributions of C 15–C 20 n-alkanes with no even/odd carbon number preference in vials and filters, respectively. These n-alkane distributions may even dominate the chromatographic profiles of the aliphatic hydrocarbon fractions corresponding to long-term stored filters. Decay of the polycyclic aromatic hydrocarbons of lower stability, e.g. 4(H)-cyclopenta[ cd]pyrene and benzo[ a]pyrene, is also observed in the filters. These de novo-produced n-alkane and iso- and anteisoalkane distributions occur at the initial stages of transformation, providing a useful tool for the detection of this type of post-sampling process.