Aircraft Instrument for Comprehensive Characterization of Aerosol Optical Properties, Part 2: Black and Brown Carbon Absorption and Absorption Enhancement Measured with Photo Acoustic Spectroscopy

This paper describes the design and performance of a photo-acoustic aerosol absorption spectrometer (PAS) built for operation on a research aircraft platform. The PAS instrument is capable of measuring dry absorption at 659 nm, 532 nm, and 404 nm, and absorption enhancement due to coatings at 532 nm and 404 nm. The measurement accuracy for all channels is < = 10% and inflight 1 Hz sensitivities lie within the range of 0.5-1.5 Mm(-1). PAS measurements of calibrated absorbing aerosol samples are shown to be consistent with measurements made by a previous generation single channel photo-acoustic instrument. Aircraft data collected during a recent field campaign in California are used to demonstrate the capabilities of the PAS. In combination with an aircraft cavity ring down aerosol extinction spectrometer described in a companion paper, the new PAS instrument provides a sensitive airborne in-situ characterization of aerosol optics.