Accurate Measurement of the Optical Properties of Single AerosolParticles Using Cavity Ring-Down Spectroscopy

New approaches for the sensitive and accuratequantification of aerosol optical properties are needed to improvethe current understanding of the unique physical chemistry ofairborne particles and to explore their roles infields as diverse aschemical manufacturing, healthcare, and atmospheric science. Wehave pioneered the use of cavity ring-down spectroscopy (CRDS),with concurrent angularly resolved elastic light scattering measure-ments, to interrogate the optical properties of single aerosolparticles levitated in optical and electrodynamic traps. Thisapproach enables the robust quantification of optical propertiessuch as extinction cross sections for individual particles of knownsize. Our measurements can now distinguish the scattering andabsorption contributions to the overall light extinction, from which the real and imaginary components of the complex refractiveindices can be retrieved and linked to chemical composition. In this Feature Article, we show that this innovative measurementplatform enables accurate and precise optical measurements for spherical and nonspherical particles, whether nonabsorbing orabsorbing at the CRDS probe wavelength. We discuss the current limitations of our approach and the key challenges in physical andatmospheric chemistry that can now be addressed by CRDS measurements for single aerosol particles levitated in controlledenvironments.

Automated summary

This article introduces a new method for quantifying the optical properties of aerosols, using CRDS combined with angularly resolved elastic light scattering measurements, to accurately measure the optical properties of individual aerosol particles, which helps to understand the role of aerosols in different fields.