Atmospheric photochemistry at a fatty acid–coated air-water interface

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