Abstract
Aerosol refractive index (RI) is related to particle composition and density, is used in optical spectroscopy studies to probe aerosol physiochemical properties during chemical reactions and gas-pa...
Highlights
Refractive index (RI, m) is an intrinsic microphysical property related to the density, molecular weight and polarizability of a substance (Liu and Daum 2008)
As found for our ammonium sulfate (AS) retrievals, the n658 precision is better than that for n405, associated with the CPC sampling directly from the exhaust of the 658-nm photoacoustic spectroscopy (PAS) channel and a 15% lower uncertainty in the 658-nm ring-down times compared to those measured for the 405-nm cavity ring-down spectroscopy (CRDS)
For non-absorbing AS, we measured n405 and n658 to a precision of 2.1% and 0.3%, respectively, while k was retrieved to a precision of better than 0.001, i.e., to within the step size for k used in our grid-search fit routine
Summary
Refractive index (RI, m) is an intrinsic microphysical property related to the density, molecular weight and polarizability of a substance (Liu and Daum 2008). Careful laboratory measurements of one or a combination of cross sections for aerosols of controlled size, shape and structure facilitate the determination of RI using inverse retrieval methods (Browne et al 2019; Radney and Zangmeister 2018; Cotterell et al 2016; 2017; Bluvshtein et al 2016; Zarzana et al 2012) These measurements involve passing an aerosol ensemble through a differential mobility analyzer that selects particles based on their electrical mobility, with mobility-selected aerosols passed onto optical spectrometers for characterizing the extinction, scattering or absorption coefficient (a). No study has assessed comprehensively the sensitivity and accuracy of n and k retrievals using combined CRDS-PAS measurements for mobility-selected aerosols with a retrieval algorithm fully accounting for the presence of multiply charged particles. This is the first study testing predictive RI mixing rules for non-aqueous internally mixed light absorbing aerosols
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