Quantification of source specific black carbon scavenging using an aethalometer and a disdrometer.

Abstract Aerosol black carbon (BC) is the second strongest contributor to global warming, after CO 2 , and it is linked to many adverse health effects. A sampling campaign of 15 months was carried out in León (Spain) in order to evaluate the scavenging of BC with an ensemble aethalometer-disdrometer. The aethalometer provides the concentration of equivalent black carbon (eBC), and the disdrometer, the raindrop size distribution. A total of seventy-five rain events were studied and in 73% of them there was an effective (eBC initial > eBC final) scavenging, with a mean decrease of 48 ± 37% in long rain events (>8 h) and 39 ± 38% in short rain events. The scavenging of BC is strongly related to its source. Thus, the scavenging coefficient (SC) mean value of the BC from fossil fuel (eBC ff) for short and long rain events was 5.1 10⁻⁵ and 1.3 10⁻⁵ s⁻¹, respectively. For the BC from biomass burning (eBC bb), the SC values were 1.6 10⁻⁴ and 2.8 10⁻⁵ s⁻¹ in short and long events, respectively. There was a significant positive correlation between the SC and the number of drops with diameters between 0.375 and 2.5 mm. Rain scavenging of eBC was analyzed depending on the air mass origin obtaining an effective scavenging for air masses from Atlantic, Arctic and Africa. A linear model (R² = 0.72) was built to estimate the ΔeBC values with variables from an aethalometer, a disdrometer and a weather station: eBC concentration before rain, swept volume and precipitation accumulated. A Kolmogorov-Smirnov statistical test confirmed the goodness of fit of the model to the measured data. Graphical abstract Image 1 Highlights • Hourly measures were taken of black carbon and rain during 15 months in León, Spain. • 70% of the rain events showed an effective scavenging (37% eBC decrease). • The scavenging coefficient for short rain events is 3 times the one for long events. • The scavenging was different according to specific BC source. • A model for rain scavenging of BC with aethalometer and disdrometer data was built. The combination of aethalometer and disdrometer measurements reveals that the scavenging of BC depends strongly on the BC source (biomass burning or fossil fuel combustion). [ABSTRACT FROM AUTHOR]