Use of diagnostic ratios for studying source apportionment and reactivity of ambient polycyclic aromatic hydrocarbons over Central Europe

Abstract

Ratios of levels of 9 polycyclic aromatic hydrocarbons (PAHs) in air at central European sites during 1996–2008 were used to assess the suitability of 5 commonly used diagnostic ratios (DRs) for PAH source apportionment. DRs derived from a detailed literature study on emission factors were reflected in ambient air samples only at sites located near major sources. A significant seasonality was observed in a long-term time series of ambient DRs at a background site indicating possible capability of this method to reflect changes in source characteristics. The results of a mass balance study suggest that current knowledge of PAH reactivities is insufficient for a source apportionment based on DRs at receptor sites, even when limited to major types of PAH sources. However, DRs could be used to narrow down ozone and hydroxyl radical reaction rate coefficients’ uncertainties: kO3(2) of pyrene and benzo(ghi)perylene in the particulate phase seem to be ≤ 10% of the highest rate coefficient measured using model aerosols in the laboratory and kO3(2) of indeno(1,2,3-cd)pyrene in the gas phase could be higher than previously estimated by three orders of magnitude. The suitability of DRs for source apportionment at (especially background) receptor sites cannot be expected in the general case. However, measurements carried out close to sources are in accordance with literature data suggesting that the ratios of benzo(a)anthracene/(benzo(a)anthracene + chrysene) and indeno(123cd)pyrene/(indeno(123cd)pyrene + benzo(ghi)perylene) are capable of distinguishing between traffic and residential heating, while the ratio of anthracene/(anthracene + phenanthrene) was the least useful DR due to its low variability.