LAUSR

Abstract A one-year black carbon (BC) experimental study was performed at three different locations (urban traffic, urban background, rural) in Spain with different equivalent BC (eBC) source characteristics by means of multi-wavelength Aethalometers. The Aethalometer model was used for the source apportionment study, based on the difference in absorption spectral dependence of emissions from biomass burning (bb) and fossil fuel (ff) combustion. Most studies use a single bb and ff absorption Angstrom exponent (AAE) pair (AAE bb and AAE ff ), however in this work we use a range of AAE values associated with fossil fuel and biomass burning based on the available measurements, which represents more properly all conditions. A sensitivity analysis of the source specific AAE was carried out to determine the most appropriate AAE values, being site dependent and seasonally variable. Here we present a methodology for the determination of the ranges of AAE bb and AAE ff by evaluating the correlations between the source apportionment of eBC using the Aethalometer model with four biomass burning tracers measured at the rural site. The best combination was AAE bb  = [1.63–1.74] and AAE ff  = [0.97–1.12]. Mean eBC values (±SD) obtained during the period of study were 3.70 ± 3.73 μg m −3 at the traffic urban site, 2.33 ± 2.96 μg m −3 at the urban background location, and 2.61 ± 5.04 μg m −3 in the rural area. High contributions of eBC to the PM 10 mass were found (values up to 21% in winter), but with high eBC/PM 10 variability. The hourly mean eBC ff and eBC bb concentrations varied from 0 to 51 μg m −3 and from 0 to 50 μg m −3 at the three sites, respectively, exhibiting distinct seasonal and daily patterns. The fossil fuel combustion was the dominant eBC source at the urban sites, while biomass burning dominated during the cold season (88% of eBC bb ) in the rural area. Daily PM 2.5 and PM 10 samples were collected using high-volume air samplers and analyzed for OC and EC. Analysis of biomass burning tracers and organic (OC) and elemental (EC) carbon in the rural area indicate that biomass combustion is the main source, while OC and EC indicate a lower influence of this source at the urban site.