Amplification of light within aerosol particles accelerates in-particle photochemistry

Optical confinement (OC) structures the optical field and amplifies light intensity inside atmospheric aerosol particles, with major consequences for sunlight-driven aerosol chemistry. Although theorized, the OC-induced spatial structuring has so far defied experimental observation. Here, x-ray spectromicroscopic imaging complemented by modeling provides direct evidence for OC-induced patterning inside photoactive particles. Single iron(III)-citrate particles were probed using the iron oxidation state as a photochemical marker. Based on these results, we predict an overall acceleration of photochemical reactions by a factor of two to three for most classes of atmospheric aerosol particles. Rotation of free aerosol particles and intraparticle molecular transport generally accelerate the photochemistry. Given the prevalence of OC effects, their influence on aerosol particle photochemistry should be considered by atmospheric models.

Automated summary

Direct evidence of optical confinement-induced patterning inside aerosol particles is provided using x-ray spectromicroscopic imaging and modeling. The study found that photochemical reactions in most aerosol particles are accelerated by optical confinement effects, with rotation of free aerosol particles and intraparticle molecular transport further enhancing the photochemistry. Atmospheric models should consider the influence of optical confinement effects on aerosol particle photochemistry.