delta C-13 values of coal-derived PAHs from different processes and their application to source apportionment

The C-13/C-12 isotopic ratios for coal-derived polycyclic aromatic hydrocar bons (PAHs) from a number of processes encompassing low and high temperatur e carbonisation. gasification and combustion have been determined using gas chromatography-isotope ratio mass spectrometry (delta(13)C GC-IRMS). The r esults, in conjunction with those for PAHs released under controlled labora tory pyrolysis conditions, indicate that the primary control on the isotopi c values of coal-derived PAHs is likely to be the extent of ring growth req uired to form PAHs during processing. Thus, for relatively mild conversion processes such as low temperature carbonisation where the major aromatics a re alkyl substituted 2-3 ring PAHs, the isotopic signatures are similar to those of the parent coals (-24 to -25 parts per thousand for UK bituminous coals). However, the delta(13)C values for the PhHs become lighter in going to high temperature carbonisation (-25 to 270 parts per thousand), gasific ation (-27 to 29 parts per thousand for old Town gas plants in the UK) and combustion (-29 to -31%0) as the extent of ring condensation increases and confirming that the PAHs are not released as primary volatiles. To demonstr ate the potential of applying these differences to source apportion environ mental PAHs where major inputs from coals can be expected, soil and vegetat ion samples taken close to a low temperature carbonisation plant (Bolsover, North Derbyshire) have been analysed. In addition to low temperature coal tar, significant inputs of PAHs from transport fuels, high temperature carb onisation and possibly combustion (coal/biomass) have been inferred from th e isotopic ratios, taken in conjunction with the differences in alkyl subst itution patterns. (C) 1999 Elsevier Science Ltd. All rights reserved.