Source apportionment of the carbonaceous aerosol in Norway – quantitative estimates based on ¹⁴C, thermal-optical and organic tracer analysis

Abstract. In the present study, source apportionment of the ambient summer and winter time particulate carbonaceous matter (PCM) in aerosol particles (PM₁ and PM₁₀) has been conducted for the Norwegian urban and rural background environment. Statistical treatment of data from thermal-optical, ¹⁴C and organic tracer analysis using Latin Hypercube Sampling has allowed for quantitative estimates of seven different sources contributing to the ambient carbonaceous aerosol. These are: elemental carbon from combustion of biomass (EC_bb) and fossil fuel (EC_ff), primary and secondary organic carbon arising from combustion of biomass (OC_bb) and fossil fuel (OC_ff), primary biological aerosol particles (OC_PBAP, which includes plant debris, OC_pbc, and fungal spores, OC_pbs), and secondary organic aerosol from biogenic precursors (OC_BSOA).

Our results show that emissions from natural sources were particularly abundant in summer, and with a more pronounced influence at the rural compared to the urban background site. 80% of total carbon (TC_p, corrected for the positive artefact) in PM₁₀ and ca. 70% of TC_pin PM₁ could be attributed to natural sources at the rural background site in summer. Natural sources account for about 50% of TC_p in PM₁₀ at the urban background site as well. The natural source contribution was always dominated by OC_BSOA, regardless of season, site and size fraction. During winter anthropogenic sources totally dominated the carbonaceous aerosol (80–90%). Combustion of biomass contributed slightly more than fossil-fuel sources in winter, whereas emissions from fossil-fuel sources were more abundant in summer.

Mass closure calculations show that PCM made significant contributions to the mass concentration of the ambient PM regardless of size fraction, season, and site. A larger fraction of PM₁ (ca. 40–60%) was accounted for by carbonaceous matter compared to PM₁₀ (ca. 40–50%), but only by a small margin. In general, there were no pronounced differences in the relative contribution of carbonaceous matter to PM with respect to season or between the two sites.