Analysing the light-to-heat conversion of Black Carbon agglomerates to interpret results from different light absorption instruments

Abstract. Black Carbon (BC) is an important pollutant due to its climatic and health effects. Most BC detection devices rely on light absorption but measured BC concentrations may vary due to different light settings. Here, we propose a theoretical model that can be used to interpret and correct the signal of optoacoustic devices. It is based on Laser Induced Incandescence (LII) theory, but advancing the description of light absorption and heat conduction by agglomerate particles. It is validated with existing experimental literature data and with new optoacoustic measurements. The model predicts that high fractal dimensions are associated with weaker signal and that the volume to surface ratio can be used as a signal reduction predictor. Then, we introduce a dimensionless metric which very well corelates with the measured signal from BC particles. The new metric can be used to harmonize measurements from different devices and also extract particle morphological information from optoacoustic signals.