Source apportionment of particulate matter in Europe: A review of methods and results

European publications dealing with source apportionment (SA) of atmospheric particulate matter (PM) between 1987 and 2007 were reviewed in the present work, with a focus on methods and results. The main goal of this meta-analysis was to provide a review of the most commonly used SA methods in Europe, their comparability and results, and to evaluate current trends and identify possible gaps of the methods and future research directions. Our analysis showed that studies throughout Europe agree on the identification of four main source types (PM10PM10 and PM2.5PM2.5): a vehicular source (traced by carbon/Fe/Ba/Zn/Cu), a crustal source (Al/Si/Ca/Fe), a sea-salt source (Na/Cl/Mg), and a mixed industrial/fuel-oil combustion (V/Ni/SO42-) and a secondary aerosol (SO42-/NO3-/NH4+) source (the latter two probably representing the same source type). Their contributions to bulk PM levels varied widely at different monitoring sites, and showed clear spatial patterns in the cases of the crustal and sea-salt sources. Other specific sources such as biomass combustion or shipping emissions were rarely identified, even though they may contribute significantly to PM levels in specific locations.