Fossil and non-fossil sources of organic carbon (OC) and elemental carbon (EC) in Göteborg, Sweden

Abstract

Abstract. Particulate matter was collected at an urban site in Göteborg (Sweden) in February/March 2005 and in June/July 2006. Additional samples were collected at a rural site for the winter period. Total carbon (TC) concentrations were 2.1–3.6 μg m−3, 1.8–1.9 μg m−3, and 2.2–3.0 μg m−3 for urban/winter, rural/winter, and urban/summer conditions, respectively. Elemental carbon (EC), organic carbon (OC), water-insoluble OC (WINSOC), and water-soluble OC (WSOC) were analyzed for 14C in order to distinguish fossil from non-fossil emissions. As wood burning is the single major source of non-fossil EC, its contribution can be quantified directly. For non-fossil OC, the wood-burning fraction was determined independently by levoglucosan and 14C analysis and combined using Latin-hypercube sampling (LHS). For the winter period, the relative contribution of EC from wood burning to the total EC was >3 times higher at the rural site compared to the urban site, whereas the absolute concentrations of EC from wood burning were elevated only moderately at the rural compared to the urban site. Thus, the urban site is substantially more influenced by fossil EC emissions. For summer, biogenic emissions dominated OC concentrations most likely due to secondary organic aerosol (SOA) formation. During both seasons, a more pronounced fossil signal was observed for Göteborg than has previously been reported for Zurich, Switzerland. Analysis of air mass origin using back trajectories suggests that the fossil impact was larger when local sources dominated, whereas long-range transport caused an enhanced non-fossil signal. In comparison to other European locations, concentrations of levoglucosan and other monosaccharide anhydrides were low for the urban and the rural site in the area of Göteborg during winter.

Radiocarbon Analysis of Carbonaceous Aerosols: Recent Developments

“…[12] Studies from Los Angeles and Denver in the 1980s and 1990s showed that TC may originate from fossil sources by up to >70% in large U.S. cities. [16,17] Zurich and Gothenburg as European urban sites show smaller fossil contributions of ~50%, [14,15,22] which are only slightly higher than for most of the investigated European rural sites. [22,30,31] During summer, EC is nearly exclusively of fossil origin with soot production from all kinds of diesel engines as the most important source.…”

“…[6] For the isolation of both fractions for 14 C analysis, however, such corrections cannot be used. [22] Therefore, the two-step oxidation of OC and EC in pure oxygen is the method of choice, as it is much less prone to charring. [20,22] Further reduction of charring for the isolation of EC is achieved by water extraction of the filters prior to the thermal treatment.…”

“…[20,22] Further reduction of charring for the isolation of EC is achieved by water extraction of the filters prior to the thermal treatment. [10,14,22] This allows the removal of water-soluble inorganic and organic compounds from the filters, which support the artificial production of EC from OC during analysis, whereas EC remains completely on the filter. Therefore, the two-step heating system for the EC/OC determination of radiocarbon in the environment (THEODORE, Fig.…”

“…OC is oxidized from the quartz filters at 340 °C in a stream of pure oxygen during 10 min. [14,22] EC is oxidized at 650 °C after complete elimination of OC and interfering water-soluble inorganic compounds, which is done by extraction with diluted hydrochloric acid and water followed by pre-heating in air at 370-390 °C for 4 h. CO 2 evolving from OC and EC is cryo-trapped and sealed in ampoules for 14 C measurement.…”

“…Previously, [15] EC wood determinations were used in combination with EC/OC emission ratios for wood burning from the literature. Later, [22] this approach was refined by additional measurements of levoglucosan, a prominent tracer substance of wood burning. [31] This later improvement generates more robust results than the earlier one, as it relies on two independent tracers of OC wood , namely EC wood and levoglucosan.…”