10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


Comparing Refractive Index Retrievals of Size- and Mass-Selected Particles to Full Distribution Measurements: A Metrology Perspective

JAMES RADNEY, Christopher Zangmeister, National Institute of Standards and Technology

     Abstract Number: 952
     Working Group: Instrumentation

Abstract
Retrieving refractive indices from measured optical and size and/or mass data for both ambient and laboratory aerosols has found significant use in recent years. Here, we compare results for refractive indices retrieved from measurements of size- and mass-selected particles to those using the full distribution (i.e. measurements typically performed in the laboratory versus field, respectively) with particles of various morphologies and compositions: single component (ammonium sulfate and nigrosin), homogeneous mixtures of ammonium sulfate and nigrosin at multiple mixing ratios and core-shell particles at multiple mixing ratios of ammonium sulfate and black carbon. Extinction and absorption coefficients, aerosol size (electrical mobility), mass and number concentrations were measured using cavity ring-down and photoacoustic spectrometers, a differential mobility analyzer, an aerosol particle mass analyzer and a condensation particle counter, respectively. We find that the two methods compare reasonably well for single component aerosols (≈ 5 % and 25 % deviations in the real and imaginary refractive indices, respectively) with significantly larger deviations in the imaginary component for the homogeneous mixtures and core-shell particles (≈ 50 %). Notably, neither measurement (size/mass selected or full distribution) can quantitatively capture the size dependence of the absorption cross sections to better than 30 % for the homogeneous mixtures or core-shell particles. Last, we will discuss the benefits, limitations and sensitivities of each method relative to all the measured parameters (extinction, absorption, number concentration, size and effective density).