Optical properties of absorbing and non-absorbing aerosols retrieved by cavity ring down (CRD) spectroscopy

[摘要] Application of cavity ring down (CRD) spectrometry for measuring the opticalproperties of pure and mixed laboratory-generated aerosols is presented. Theextinction coefficient (α_ext), extinction cross section(σ_ext) and extinction efficiency (Q_ext) were measured forpolystyrene spheres (PSS), ammonium sulphate ((NH₄)₂(SO₄),sodium chloride (NaCl), glutaric acid (GA), and Rhodamine-590 aerosols. Therefractive indices of the different aerosols were retrieved by comparing themeasured extinction efficiency of each aerosol type to the extinctionpredicted by Mie theory. Aerosols composed of sodium chloride and glutaricacid in different mixing ratios were used as model for mixed aerosols of twonon-absorbing materials, and their extinction and complex refractive indexwere derived. Aerosols composed of Rhodamine-590 and ammonium sulphate indifferent mixing ratios were used as model for mixing of absorbing andnon-absorbing species, and their optical properties were derived. Therefractive indices of the mixed aerosols were also calculated by variousoptical mixing rules. We found that fornon-absorbing mixtures, the linear rule, Maxwell-Garnett rule, and extendedeffective medium approximation (EEMA), givecomparable results, with the linear mixing rule giving a slightly better fitthan the others. Overall, calculations for the mixed aerosols are not asgood as for single component aerosols. For absorbing mixtures, thedifferences between the refractive indices calculated using the mixing rulesand those retrieved by CRD are generally higher.

[学科分类] 大气科学