Filter-free measurements of black carbon absorption using photoacoustic spectroscopy

A photoacoustic (PA) spectrophone was developed for filter-free measurement of black carbon (BC) mass absorption coefficient (MAC) in the spectral region of similar to 442 nm using a blue diode laser. The PA sensor was characterized and calibrated using NO2 at standard calibrated concentrations, as well as at indoor and outdoor air concentrations via a side-by-side intercomparison with a commercial NOx analyzer. Black carbon (graphite) and volcanic ash samples were measured under laboratory condition. MAC of BC and volcanic ash sample were determined based on the measured particles optical absorption coefficient by the PA spectrophone, in combination with the mass concentration measured using a scanning mobility particle sizer (SMPS). A minimum detectable absorption coefficient (1 sigma) of similar to 1.2 Mm(-1) for BC was achieved with a time solution of 1 second.