Oxidation of atmospheric aerosol can produce cloud condensation nuclei capable of changing the reflectivity and lifetime of clouds. The oxidation of organic film on atmospheric mineral dust may activate mineral dust into cloud droplets. To assess the atmospheric importance the chemical lifetime of the organic material to a common atmospheric oxidant (OH radical) must be measured and compared to deposition lifetime of the mineral aerosol (4-10 days). The chemical lifetime will be assessed by measuring the rate of oxidation of a bilayer of a lipid DPPC from the solid-liquid interface of a silica mineral window, using neutron reflection. Selective deuteration, the ability to measure film thickness and amount of material at the solid-liquid interface will allow chemical mechanism to be deduced. Preliminary studies show the experiment viable, and these data are needed for publication.