Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot TörökSandra MalmborgVilhelm B. SimonssonJohan ErikssonAxel MartinssonJohan MannazhiManu PagelsJoakim BengtssonPer-Erik 2018 <p>In this work, a mini-CAST soot generator was used to produce soot with different optical and physicochemical characteristics. Absorption Ångström exponents (<i>AAE</i>) expressing the absorption wavelength dependence were assessed by multiwavelength <i>in-situ</i> and filter-based (aethalometer) laser extinction. The two optical techniques showed good agreement. For the chosen mini-CAST operating conditions, <i>AAE</i>s between 1 and 3.5 were found. Soot with high mass-fractions of organic carbon (OC) and pyrolytic carbon (PC) determined with thermal optical analysis were associated with <i>AAE</i>s significantly higher than 1. Heating to 250 and 500°C removed the majority of polycyclic aromatic hydrocarbons. However, the thermal-optical analysis revealed that OC and PC were abundant in the soot with <i>AAE</i> > 2 also after heating the aerosol. Analysis of mass absorption cross section ratios for elemental carbon and OC indicated that elevated <i>AAEs</i> also after heating to 500°C could be related to persistent OC and PC components and/or the refractory soot. By comparing the mini-CAST soot optical properties with soot properties derived from <i>in-situ</i> extinction measurements in a premixed flame, mini-CAST soot with a higher <i>AAE</i> could be identified as less mature soot.</p> <p>Copyright © 2018 The Authors</p>