Differences in the Occurrence of Polycyclic Aromatic Hydrocarbons and Geochemical Markers in the Dust Emitted from Various Coal-Fired Boilers

Abstract

Organic compounds occurring in emitted fly ashes from bituminous coal and bituminous coal and biomass combustion in various boilers were qualitatively and quantitatively analyzed. Gas chromatography with a flame ionization detector (GC-FID) was applied to polycyclic aromatic hydrocarbons (PAHs) and gas chromatography–mass spectrometry (GC-MS) for geochemical markers, such as n-alkanes, acyclic isoprenoids, steranes, pentacyclic triterpenoids (hopanes and moretanes), alkyl PAHs, and biomass markers. It was found that distributions of geochemical markers and presence are well preserved in fly ash. Particularly in fly ash from boilers of older types, thermal changes are small and mainly affect compounds of low molecular weight whereas, in fly ash from a fluidized bed combustion boiler, most geochemical markers were destroyed. It is possible that high molecular weight compounds survived the high temperature process when adsorbed in unburned or coked coal and/or biomass particles included in the dust emitted. PAH group profiles were made, while PAHs diagnostic indices and geochemical marker ratios were calculated and compared with literature data. Fly ash from coal and biomass combustion contains the highest PAH concentrations and shows the highest values of toxic equivalence (TEQ) factors among all boilers investigated. The results indicate that, whereas the distributions and ratios of geochemical markers are close to those of bituminous coals and can be applied to indicate source fuels in particulate matter, there are high differences between the values of diagnostic ratios found in this project and literature data. This indicates that PAH diagnostic ratios should be applied with care and confirmed by other data, e.g., those from geochemical markers, which may be recommended for research on the type of emission sources of particulate matter into the air.