Contribution of coal combustion to black carbon: coupling tracers with the aethalometer model

Abstract

Black carbon (BC) aerosol characteristics have been analysed from January 2016 to March 2017 in an urban background area (León, Spain), located in a coal-mining region, where this fuel is commonly used. The monthly and seasonal variations of BC and source contributions were examined. The mean equivalent BC concentration (eBC) during cold and warm months were 1.0±0.5 and 0.6±0.2 μg m-3, respectively. eBC can be further divided into eBCff (eBC from liquid fossil fuel) and eBCbb+cc (eBC from biomass burning plus coal combustion), with mean annual values of 0.6±0.3 and 0.3±0.3 μg m 3 (cold months) and 0.4±0.2 μg m 3 and 0.1±0.1 μg m 3 (warm months), respectively. The eBC obtained from the aethalometer and the elemental carbon (EC) quantified through a Thermal Optical Transmittance method presented a significant strong positive correlation in both warm (r=0.82) and cold (r=0.88) periods. A mass absorption cross-section (MAC) of 4.46±0.16 between two techniques has been obtained. In the cold period, a multilinear regression model to decouple eBCbb from eBCcc was established (r2=0.85) based on two tracers: arsenic for coal combustion and potassium for biomass burning. The model application enabled us to distinguish the contributions to eBCbb+cc (as a function of the variance explained by the tracers) in the cold period: 74% from biomass burning and 26% from coal combustion. The highest eBCcc concentration was estimated for December 2016 and January 2017 (0.18 μg m 3). This result was supported by the Absorption Ångström Exponent (AAE), which showed the maximum value in January 2017 (1.43±0.37) due to the high biomass burning and coal combustion contributions.