Black carbon (BC) and brown carbon (BrC) aerosols are widely studied components of atmospheric aerosol because they can absorb solar radiation and heat the atmosphere, causing positive radiative forcing of the climate. Although BC and BrC are very important for climate, they are poorly represented in atmospheric models. This is in part due to the complex microphysical properties of BC and the lack of accurate refractive index (RI) descriptions for both BC and BrC.
SASSO capitalized on a unique combination of new technical and methodological developments at the University of Manchester and the University of Exeter to generate experimental data on a variety of soot types, providing much greater constraints on optical properties than previously possible. Specifically, SASSO used the Aerodynamic Aerosol Classifier (AAC) for size selection of emissions from wood burning, diesel combustion, and secondary organic aerosol (SOA) formation, prior to optical measurements using cavity ring-down and photoacoustic spectroscopy with the EXtinction, SCattering and Absorption of Light for AirBorne Aerosol Research (EXSCALABAR) instrumentation, custom-built by the Met Office.
In addition, to test the "lensing effect," non-absorbing and weakly absorbing organic materials were condensed onto BC to form coated soot particles. The mass concentration of black carbon aerosol was measured using the Single Particle Soot Photometer (SP2), and chemical information was obtained via Aerosol Mass Spectrometry (AMS), allowing different optical models for mixed particles to be evaluated.