Measurements of the Real and Imaginary Refractive Index of Single Aerosol Particles

Rose E. Willoughby1, Michael I. Cotterell1,2,3, Bryan R. Bzdek1, Hongze Lin4, Andrew J. Orr-Ewing1 and Jonathan P. Reid1

1 School of Chemistry, University of Bristol, BS8 1TS, UK

2 College for Engineering, Mathematics and Physical Sciences, University of Exeter, EX4 4QF, UK

3 Aerosol Observation Based Research, Met Office, EX1 3PB, UK

4 College of Optical Science and Engineering, Zhejiang University, Hangzhou 310058, China

Summary

Single, hygroscopic aerosol particles were studied at a number of wavelengths of illumination and at varied relative humidity (RH) (and therefore varied composition) to provide accurate parameterisations of the optical properties of surrogates of atmospheric aerosol. In this work, particles were optically trapped with a Bessel laser beam and the particle refractive index and size were probed with cavity ring-down spectroscopy and phase function measurements. A parameterisation of the real refractive index of aqueous inorganic aerosol and a new method to retrieve the imaginary refractive index will be presented.