The reactive uptake of the NO₃ radical by liquid and frozen organics was studied in a rotating wall flow tube coupled to a White cell. The organic liquids used included alkanes, alkenes, an alcohol, and carboxylic acids with conjugated and nonconjugated unsaturated bonds.. The reactive uptake coefficients, γ, of NO₃ on n-hexadecane, 1-octadecene, 1-hexadecene, cis + trans 7-tetradecene, n-octanoic acid, 2,2,4,4,6,8,8 heptamethyl nonane, 1-octanol, cis, trans 9,11 and 10,12 octadecadienoic acid, cis-9, cis-12 octadecadienoic acid were determined. The reactive uptake coefficients measured with the organic liquids varied from 1.4 × 10⁻³ to 1.5 × 10⁻². The uptake coefficients of NO₃ by n-hexadecane and n-octanoic acid decreased by a factor of ∼5 upon freezing. This behavior is explained by reaction occurring in the bulk of the organic liquid as well as on the surface. For the rest of the compounds the change in values of γ upon freezing of the liquids was within the experimental uncertainty. This is attributed to predominant uptake of NO₃ by the top few molecular surface layers of the organic substrate and continuous replenishment of the surface layer by evaporation and/or mobility of the surface. These conclusions are corroborated by estimation of the diffuso-reactive length and solubility constant of NO₃ in these liquids. The reactivity of NO₃ with the organic surfaces is shown to correlate well with the known gas-phase chemistry of NO₃. The effect on the atmospheric chemistry of the NO₃ radical due to its interaction with organic aerosols is studied using an atmospheric box model applying realistic atmospheric scenarios. The inclusion of NO₃ uptake on organic aerosol can decrease the NO₃ lifetime by 10% or more.