A 480 L evacuable reaction chamber, equipped with FT-IR spectroscopy on-line and ion chromatography off-line, has been used to study the gas phase reaction between the nitrate radical, NOa, and the reduced organic sulphur compounds CH~CHZSH, ( C H ~C H ~Z S , (CH~CHZ)ZSZ, and CH&H2SCH3 in air. The products CHaCHZS03H, SOZ, HzS04, CH3CH0, and CH~CHZONOZ were identified and quantified in the reactions of the first three compounds, CH~CHZSH, (CH3CH2),S, and (CH~CHZ)&. The reaction products were CH&HZS03H, CHaSOaH, SOZ, HzS04, CH3CH0, and CH20 in the reaction of CH3CH2SCH3. On the basis ofidentified reaction products and intermediates observed in the infrared spectra, mechanisms are proposed for the reactions between the NO3 radical and the four reduced organic sulphur compounds. The results of this study, together with those from previous experiments performed in this laboratory on CH3SCH3, CHaSH, and CH3SSCH3 lead to the conclusion that all these species, in the reaction with the NO3 radical, follow a similar degradation mechanism producing SO?, H2SO4, R -S03H, R-CHO, and R-CHZONO~, as the main reaction products. The inital step of the reaction of NO3 with R-S-R and R-S-H type (R=CH3, CHZCH3) reduced organic sulphur compounds was found to be H-atom abstraction, probably after the formation of an initial adduct. For the reaction between NOs and R-S-S-R type compounds, evidence for an additiondecomposition reaction, as the initial steps, was obtained. R-s., R-S(O)., and R-S(Oh. appear to be formed as intermediates in all the reactions.