We propose a simultaneous neutron reflectometry (NR)/attenuated total reflection (ATR) infra-red spectroscopy experiment on spin-coated thin films of self-assembled fatty acids on Si wavers as proxies for atmospheric aerosols. Key aims are to (i) quantify the effect of film thickness on kinetics of nitrate-radical initiated oxidation and (ii) explore the humidity response of lyotropic phases by controlling the humidity with a bespoke humidity control system. The reproducible film thickness achieved by spin coating lends itself to a thorough film thickness-kinetics study much needed in the literature. This experiment will build on our previous qualitative findings (Nat Commun, 2017) and on publications as a result of previous NR beamtime studying surfactants at the air-water interface. It is synergistically linked to a DLS application on ozonolysis of spin-coated films.