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 (D-m) = 350 nm, which is used as a calibration surrogate. Based on the Allan variance analysis, detection limits (2 sigma) 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 (c) 2018 American Association for Aerosol Research
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