Articles | Volume 14, issue 24
Atmos. Chem. Phys., 14, 13551–13570, 2014
Atmos. Chem. Phys., 14, 13551–13570, 2014

Research article 19 Dec 2014

Research article | 19 Dec 2014

Radiocarbon analysis of elemental and organic carbon in Switzerland during winter-smog episodes from 2008 to 2012 – Part 1: Source apportionment and spatial variability

P. Zotter1, V. G. Ciobanu1,*, Y. L. Zhang1,2,3,4,**, I. El-Haddad1, M. Macchia5, K. R. Daellenbach1, G. A. Salazar2,3, R.-J. Huang1, L. Wacker6, C. Hueglin7, A. Piazzalunga8, P. Fermo9, M. Schwikowski2,3,4, U. Baltensperger1, S. Szidat2,3, and A. S. H. Prévôt1 P. Zotter et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
  • 2Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
  • 3Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 4Laboratory of Radiochemistry and Environmental Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
  • 5CEDAD-Department of Engineering for Innovation, University of Salento, Lecce, Italy
  • 6Laboratory of Ion Beam Physics, ETH Hönggerberg, Zürich, Switzerland
  • 7Laboratory for Air Pollution and Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf, Switzerland
  • 8University of Milano Bicocca, Department of Earth and Environmental Sciences, 20126 Milano, Italy
  • 9Department of Chemistry, University of Milano, 20133 Milano, Italy
  • *now at: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • **now at: Yale-NUIST Center on Atmospheric Environmental, Nanjing University of Information Science and Technology, Nanjing, Jiangsu 210044, China

Abstract. While several studies have investigated winter-time air pollution with a wide range of concentration levels, hardly any results are available for longer time periods covering several winter-smog episodes at various locations; e.g., often only a few weeks from a single winter are investigated. Here, we present source apportionment results of winter-smog episodes from 16 air pollution monitoring stations across Switzerland from five consecutive winters. Radiocarbon (14C) analyses of the elemental (EC) and organic (OC) carbon fractions, as well as levoglucosan, major water-soluble ionic species and gas-phase pollutant measurements were used to characterize the different sources of PM10. The most important contributions to PM10 during winter-smog episodes in Switzerland were on average the secondary inorganic constituents (sum of nitrate, sulfate and ammonium = 41 ± 15%) followed by organic matter (OM) (34 ± 13%) and EC (5 ± 2%). The non-fossil fractions of OC (fNF,OC) ranged on average from 69 to 85 and 80 to 95% for stations north and south of the Alps, respectively, showing that traffic contributes on average only up to ~ 30% to OC. The non-fossil fraction of EC (fNF,EC), entirely attributable to primary wood burning, was on average 42 ± 13 and 49 ± 15% for north and south of the Alps, respectively. While a high correlation was observed between fossil EC and nitrogen oxides, both primarily emitted by traffic, these species did not significantly correlate with fossil OC (OCF), which seems to suggest that a considerable amount of OCF is secondary, from fossil precursors. Elevated fNF,EC and fNF,OC values and the high correlation of the latter with other wood burning markers, including levoglucosan and water soluble potassium (K+) indicate that residential wood burning is the major source of carbonaceous aerosols during winter-smog episodes in Switzerland. The inspection of the non-fossil OC and EC levels and the relation with levoglucosan and water-soluble K+ shows different ratios for stations north and south of the Alps (most likely because of differences in burning technologies) for these two regions in Switzerland.

Final-revised paper