Understanding the optical properties of micrometer-scale light-absorbing aerosol particles is of paramount importance in addressing key challenges in atmospheric and physical chemistry. For example, the absorption of solar radiation by atmospheric aerosols represents one of the largest uncertainties in climate models. Moreover, reaction acceleration within the unique environments of aerosol droplets cannot be replicated in bulk solutions. The causes of these reaction rate enhancements remain controversial, but ultrasensitive spectroscopic measurements of evolving aerosol optical properties should provide new insights. We demonstrate a new approach using cavity ring-down spectroscopy that allows the first direct spectroscopic quantification of the continuously evolving absorption and scattering cross sections for single, levitated, micrometer-scale particles as their size and chromophore concentration change. For two-component droplets composed of nigrosin and 1,2,6-hexanetriol, the unprecedented sensitivity of our measurements reveals the evolving real and imaginary components of the refractive index caused by changes in concentration as 1,2,6-hexanetriol slowly evaporates.
|Number of pages||7|
|Journal||Journal of Physical Chemistry A|
|Early online date||23 Feb 2022|
|Publication status||Published - 10 Mar 2022|
Bibliographical noteFunding Information:
J.W.K. and J.V.E. were supported through studentships provided by the EPSRC Centre for Doctoral Training in Aerosol Science (EP/S023593/1). M.I.C. acknowledges the NERC for the award of an Independent Research Fellowship (NE/S014314/1).
© 2022 American Chemical Society.