Calibration of a multi-pass photoacoustic spectrometer cell using light-absorbing aerosols

Nir Bluvshtein,Quanfu He,Enrico Segre,Lior Segev,Nina Hong,James N Hilfiker,Yinon Rudich,Andrea Donohue,J Michel Flores

doi:10.5194/amt-10-1203-2017

Abstract

Abstract. The multi-pass photoacoustic spectrometer (PAS) is an important tool for the direct measurement of light absorption by atmospheric aerosol. Accurate PAS measurements heavily rely on accurate calibration of their signal. Ozone is often used for calibrating PAS instruments by relating the photoacoustic signal to the absorption coefficient measured by an independent method such as cavity ring down spectroscopy (CRD-S), cavity-enhanced spectroscopy (CES) or an ozone monitor. We report here a calibration method that uses measured absorption coefficients of aerosolized, light-absorbing organic materials and offer an alternative approach to calibrate photoacoustic aerosol spectrometers at 404 nm. To implement this method, we first determined the complex refractive index of nigrosin, an organic dye, using spectroscopic ellipsometry and then used this well-characterized material as a standard material for PAS calibration.

Highlights

Light absorption by atmospheric aerosols still poses one of the greatest uncertainties associated with the effective radiative forcing due to aerosol–radiation interactions (IPCC, 2013)
Such widespread of complex refractive index (RI) values emphasizes the need for more accurate measurements for future use of nigrosin as a standard material and the limitations of the cavity ring down spectroscopy (CRD-S) method, which can benefit from a new wellestablished standard
In this study we propose a new calibration scheme for astigmatic photoacoustic spectrometer (PAS) instrument using nigrosin, a widely available water-soluble absorbing material

Summary

Introduction

Light absorption by atmospheric aerosols still poses one of the greatest uncertainties associated with the effective radiative forcing due to aerosol–radiation interactions (IPCC, 2013). Absorption of visible incoming solar radiation exerts positive radiative forcing at the top of the atmosphere due to heat transfer from light-absorbing aerosols to their surroundings. In terms of positive radiative forcing, black carbon (BC) aerosols are often considered to be second only to CO2 (Bond et al, 2013) with strong absorption throughout the solar spectrum. The atmospheric burden of BrC is estimated to be more than 3 times that of BC (Feng et al, 2013) its absorption is strongly spectral-dependent with strong absorption in the UV and visible (vis) spectrum and weak to non-absorbing in the longer wavelengths (Hoffer et al, 2004; Kirchstetter et al, 2004; Kaskaoutis et al, 2007; Sun et al, 2007; Chen and Bond, 2010; Moosmuller et al, 2011; Lack et al, 2012a)

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Conclusion