Active fatty acid layers: Saturated fatty acids are considered to be inert, but they can be surprisingly reactive when present as a coating at an air-water interface. Rossignol et al. show that nonanoic acid is photochemically active when it is present as a monolayer on a water surface (see the Perspective by Vaida). Fatty acids are ubiquitous in the environment, and their photochemical processing could have a substantial impact on local ozone and particle formation. Science , this issue p. 699 ; see also p. 650

This review paper describes briefly the cloud aqueous phase composition and deeply its reactivity in the dark and mainly under solar radiation. The role of the main oxidants (hydrogen peroxide, nitrate radical, and hydroxyl radical) is presented with a focus on the hydroxyl radical, which drives the oxidation capacity during the day. Its sources in the aqueous phase, mainly through photochemical mechanisms with H₂O₂, iron complexes, or nitrate/nitrite ions, are presented in detail. The formation rate of hydroxyl radical and its steady state concentration evaluated by different authors are listed and compared. Finally, a paragraph is also dedicated to the sinks and the reactivity of the HO^• radical with the main compounds found in the cloud aqueous phase. This review presents an assessment of the reactivity in the cloud aqueous phase and shows the significant potential impact that this medium can have on the chemistry of the atmosphere and more generally on the climate.

Atmospheric plastic pollution is now a global problem. Microplastics (MP) have been detected in urban atmospheres as well as in remote and pristine environments, showing that suspension, deposition and aeolian transport of MP should be included and considered as a major transport pathway in the plastic life cycle. This work reports an up to date review of the experimental estimation of deposition rate of MP in rural and urban environment, also analyzing the correlation with meteorological factors. Due to the limitations in sampling and instrumental methodology, little is known about MP and nanoplastics (NP) with sizes lower than 50 µm. In this review, we describe how NP could be transported for longer distances than MP, making them globally present and potentially more concentrated than MP. We highlight that it is crucial to explore new methodologies to collect and analyze NP. Future research should focus on the development of new technologies, combining the existent knowledge on nanomaterial and atmospheric particle analysis.