A single-pass RGB differential photoacoustic spectrometer (RGB-DPAS) for aerosol absorption measurement at 473, 532, and 671 nm

Abstract

In this study, we describe a newly developed three-wavelength differential photoacoustic spectrometer, which we denote RGB-DPAS, for aerosol absorption measurement in the visible spectral range: 671 nm (red), 532 nm (green), and 473 nm (blue). This instrument utilizes the differential photoacoustic spectrometric (DPAS) technique, which simultaneously measures light absorption signals due to total particulate matter + gaseous samples and those of gaseous samples alone. The difference between the photoacoustic signals recorded from the two nearly identical acoustic cells (<0.2% variability in physical dimensions) yields the aerosol photoacoustic signals at the three wavelengths. This measurement approach eliminates the interferences from light-absorbing gaseous species as well as low-frequency ambient acoustic noise. In this study, we demonstrate the linearity of the RGB-DPAS signal response to the number concentration of the synthetic carbon black particles at electrical mobility diameter (Dm) = 350 nm, which is used as a calibration surrogate. Based on the Allan variance analysis, detection limits (2σ) of 0.20 Mm−1 at 671 nm, 0.22 Mm−1 at 532 nm, and 0.90 Mm−1 at 473 nm have been achieved in 100 s data acquisition for the RGB-DPAS instrument.Copyright © 2018 American Association for Aerosol Research