Advanced source apportionment of carbonaceous aerosols by coupling offline AMS and radiocarbon size-segregated measurements over a nearly 2-year period

• Published in: Atmospheric chemistry and physics 2018-05, Vol.18 (9), p.6187-6206
• Main Authors: Vlachou, Athanasia, Daellenbach, Kaspar R, Bozzetti, Carlo, Chazeau, Benjamin, Salazar, Gary A, Szidat, Soenke, Jaffrezo, Jean-Luc, Hueglin, Christoph, Baltensperger, Urs, Haddad, Imad El, Prévôt, André S. H
• Format: Article
• Language: English
• Subjects: Aerosols; Analytical chemistry; Anthropogenic factors; Biogenic emissions; Biomass; Biomass burning; Burning; Carbon; Carbon 14; Carbon sources; Chemical composition; Chemical properties; Chemical Sciences; Combustion; Environment and Society; Environmental aspects; Environmental Sciences; Fossil fuels; Fuel combustion; Global Changes; Mass spectra; Mass spectrometry; Ocean, Atmosphere; Organic carbon; Organic chemistry; Oxidation; Oxygenation; Particulate emissions; Particulate matter; Radiocarbon dating; Sciences of the Universe; Seasonal variability; Seasonal variation; Seasonal variations; Secondary aerosols; Separation; Spring; Sulfur; Sulphur; Summer; Suspended particulate matter; Valence; Vehicle emissions; Volatility; Winter; Wood
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-18-6187-2018

Carbonaceous aerosols are related to adverse human health effects. Therefore, identification of their sources and analysis of their chemical composition is important. The offline AMS (aerosol mass spectrometer) technique offers quantitative separation of organic aerosol (OA) factors which can be related to major OA sources, either primary or secondary. While primary OA can be more clearly separated into sources, secondary (SOA) source apportionment is more challenging because different sources – anthropogenic or natural, fossil or non-fossil – can yield similar highly oxygenated mass spectra. Radiocarbon measurements provide unequivocal separation between fossil and non-fossil sources of carbon. Here we coupled these two offline methods and analysed the OA and organic carbon (OC) of different size fractions (particulate matter below 10 and 2.5 µm – PM10 and PM2.5, respectively) from the Alpine valley of Magadino (Switzerland) during the years 2013 and 2014 (219 samples). The combination of the techniques gave further insight into the characteristics of secondary OC (SOC) which was rather based on the type of SOC precursor and not on the volatility or the oxidation state of OC, as typically considered. Out of the primary sources separated in this study, biomass burning OC was the dominant one in winter, with average concentrations of 5.36 ± 2.64 µg m−3 for PM10 and 3.83 ± 1.81 µg m−3 for PM2.5, indicating that wood combustion particles were predominantly generated in the fine mode. The additional information from the size-segregated measurements revealed a primary sulfur-containing factor, mainly fossil, detected in the coarse size fraction and related to non-exhaust traffic emissions with a yearly average PM10 (PM2.5) concentration of 0.20 ± 0.24 µg m−3 (0.05 ± 0.04 µg m−3). A primary biological OC (PBOC) was also detected in the coarse mode peaking in spring and summer with a yearly average PM10 (PM2.5) concentration of 0.79 ± 0.31 µg m−3 (0.24 ± 0.20 µg m−3). The secondary OC was separated into two oxygenated, non-fossil OC factors which were identified based on their seasonal variability (i.e. summer and winter oxygenated organic carbon, OOC) and a third anthropogenic OOC factor which correlated with fossil OC mainly peaking in winter and spring, contributing on average 13 % ± 7 % (10 % ± 9 %) to the total OC in PM10 (PM2.5). The winter OOC was also connected to anthropogenic sources, contributing on average 13 % ± 13 % (6 % ± 6 %) to the total OC in PM