A new algorithm for brown and black carbon identification and organic carbon detection in fine atmospheric aerosols by a multi-wavelength Aethalometer

摘要

A novel approach for the analysis of aerosol absorption coefficientmeasurements is presented. A 7-wavelenghts aethalometer has been employed toidentify brown carbon (BrC) and black carbon (BC) and to detect organiccarbon (OC) in fine atmospheric aerosols (PM). The Magee Aethalometerestimates the BC content in atmospheric particulate by measuring the lightattenuation in the aerosols accumulated on a quartz filter, at the standardwavelength λ = 0.88 μm. The known Magee algorithm is based on the hypothesis of a massabsorption coefficient inversely proportional to the wavelength. The newalgorithm has been developed and applied to the whole spectral range; itverifies the spectral absorption behavior and, thus, it distinguishesbetween black and brown carbon. Moreover, it allows also to correct theabsorption estimation at the UV wavelength commonly used to qualitativelydetect the presence of mixed hydrocarbons. The algorithm has been applied todata collected in Agri Valley, located in Southern Italy, where torchedcrude oil undergoes a pre-treatment process.The Magee Aethalometer has been set to measure Aerosol absorptioncoefficients τ (λ, ) every 5 min. Wavelength dependence of τ (λ, ) hasbeen analyzed by a best-fit technique and, excluding UV-wavelengths, boththe absorption Angstrom coefficient α and the BC (or BrC) concentration havebeen determined. Finally, daily histograms of α provide information onoptical properties of carbonaceous aerosol, while the extrapolation atUV-wavelengths gives information on the presence of semivolatile organiccarbon (OC) particles.