Amplification of light within aerosol particles accelerates photochemical reactions

Amplification of light in atmospheric aerosol particles can affect their photochemistry, substantially accelerating sunlight-driven in-particle photochemical reactions, which are major contributors to the degradation and oxidation of matter in these particles. Although theorized, the new study provides direct evidence that the influence of optical confinement (OC) can create spatial structuring of the light intensity inside the particles and result in variations of photochemical rates. Given the newfound importance of the phenomenon on aerosol particle photochemistry, incorporating the effects of OC into atmospheric aerosol models could improve their ability to predict global chemistry and climate. Although tiny, atmospheric aerosol particles – suspensions of fine solid particles or liquid droplets in air – have a large influence on climate and air quality, and are key components of global atmospheric models. Photochemical reactions driven by aerosol exposure to sunlight are central to atmospheric chemistry, including the creation and control of pollutants and climate-influencing gases. Here, Pablo Corral Arroyo and colleagues report the effect of OC on the photochemical reactions within aerosol particles. While previous research has predicted the effects of OC on aerosol particle photochemistry, direct observation of the phenomenon has remained elusive. Using a combination of x-ray spectromicroscopic imaging and modeling of single iron(III)-citrate particles (a photochemically degrading aerosol), Corral Arroyo et al. show that aerosol particles can act as resonators for incoming solar radiation, resulting in an overall amplification and spatial structuring of light within the particles, thereby accelerating in-particle photochemistry. Using the findings, the authors predict that this could speed up photochemical reactions by a factor of two to three for most classes of atmospheric aerosol particles.