Comparison of light absorption properties for various absorbing particles

We experimentally determined optical properties of various absorbing particles such as nigrosins, black-dyed polystyrene latex, and diesel black carbon (BC). The absorption coefficient (Qabs) was measured to determine the absorption cross section (σabs) for given particle sizes. Our experimental system consists of a differential mobility analyzer (DMA), a condensation particle counter (CPC), a multi-angle absorption photometer (MAAP), an elemental carbon/organic carbon (EC/OC) analyzer, an aerosol sampler, a dilution device, and a diesel engine. We diluted the exhaust from the diesel engine in order to provide similarity to aerosol particles of accumulation mode in the atmosphere. We measured the size distribution of diesel BC using the DMA and the CPC. The mode diameter was changed as the diesel BC was grown. We measured the number concentration (N) and the absorption coefficient for black carbon using the CPC and the MAAP, respectively. Then, we obtained absorption cross sections for various particle sizes. Preliminary result showed that the absorption cross section for diesel BC having a 200-nm diameter was measured to be 1.06 × 10−14 m2/particle. For diesel BC, mass concentrations measured by the MAAP were in good agreement with those measured by the OC/EC analyzer.