Photoacoustic and nephelometric spectroscopy of aerosol optical properties with a supercontinuum light source

Abstract

Abstract.A novel multi-wavelength photoacousticnephelometer spectrometer (SC-PNS) has been developed for the optical characterization of atmospheric aerosol particles. This instrument integrates a white light supercontinuum laser with photoacoustic and nephelometric spectroscopy to measure aerosol absorption and scattering coefficients at five wavelength bands (centered at 417, 475, 542, 607, and 675 nm). These wavelength bands are selected from the continuous spectrum of the laser (ranging from 400-2200 nm) using a set of optical interference filters. Absorption and scattering measurements on laboratory-generated aerosol samples were performed sequentially at each wavelength band.To test the instrument we measured the wavelength dependence of absorption and scattering coefficients of kerosene soot and common salt aerosols. Results were favorably compared to those obtained with a commercial 3-wavelength photoacoustic and nephelometer instrument demonstrating the utility of the SC light source for studies of aerosol optical properties at selected wavelengths. Here, we discuss instrument design, development, calibration, performance and experimental results.

Measurement and modeling of the multi-wavelength optical properties of uncoated flame-generated soot

“…The measurements here are consistent with this expectation for the collapsed (coated-denuded) particles, but the nascent particles give an AAE that is somewhat larger than 1. The observed AAE values are similar to results from previous studies examining either freshly emitted soot particles or soot particles containing very little organic material (Bergstrom et al, 2002;Schnaiter et al, 2003;Kirchstetter 10 et al, 2004;Schnaiter et al, 2006;Sharma et al, 2013;You et al, 2016).…”

Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

“…SSA values are lower than those predicted by Scarnato et al (2013), due as well to the differences in the refractive indices used in the simulations. The SSA magnitude and spectral variation presented in this study are both in agreement with laboratory measurements by Sharma et al (2013). At 550 nm, SSA shows little variability in cases BL1-BL4 with an average value of 0.19 ± 0.02.…”

“…In the spectral range between 340 and 1600 nm, AAE values are consistent with observations and theoretical results with values of approximately 1, while in the spectral range between 400 and 675 nm AAE values approach 1.2 (in agreement with Lack and Langridge, 2013). The range of values of AAE, EAE and SAE is also fairly consistent with Sharma et al (2013). For example, we found a SAE average value of 1.79 ± 0.37, which is in the range of values reported by Sharma et al (2013) …”

“…The range of values of AAE, EAE and SAE is also fairly consistent with Sharma et al (2013). For example, we found a SAE average value of 1.79 ± 0.37, which is in the range of values reported by Sharma et al (2013) …”

“…Key results for bare BC aggregates include (i) a weak MAC dependency on the aggregate size, but stronger MAC dependency on the refractive index, in agreement with Berry and Percival (1986), Liu et al (2008) and Scarnato et al (2013); (ii) a strong g dependency on aggregate size; (iii) consistency between DDSCAT-predicted and observed values of AAE, EAE, SAE (e.g., Lack and Langridge, 2013) and SSA (and its spectral variability) (Sharma et al, 2013).…”