Real Time, in Situ Measurement of Aerosol Light Absorption with a New Photoacoustic Instrument: Quantification of Black and Elemental Carbon Aerosol

Abstract

A photoacoustic instrument has been developed to measure in situ light absorption by aerosol. The current lower detection limit for light absorption is 0.4 Mm−1 which corresponds to an elemental carbon mass density of ≈ 40 ng/m3 assuming an efficiency for light absorption of 10 m2/g. Calibration is performed using simple theory for the instrument along with use of a calibrated microphone and laser. Two compact, efficient lasers were used during instrument evaluation performed in the North Front Range Air Quality Study (Colorado, 1996/97). Laser wavelengths were 532 run and 685 nm, and corresponding average powers were 60 mW and 87 mW. Nearby measurements of black and elemental carbon aerosol show good correlation with the photoacoustic measurement of aerosol light absorption and shed further light on the question of absorption efficiencies of black and elemental carbon aerosol.