Abstract. The uptake of NO₃ and N₂O₅ to Saharan dust, ambient aerosols and soot was investigated using a novel and simple relative rate method with simultaneous detection of both NO₃ and N₂O₅. The use of cavity ring down spectroscopy to detect both trace gases enabled the measurements to be carried out at low mixing ratios (<500 pptv or 1×10¹⁰ molecule cm⁻³). The uptake coefficient ratio, γ(NO₃)/γ(N₂O₅), was determined to be 0.9±0.4 for Saharan dust, independent of relative humidity, NO₃ or N₂O₅ mixing ratio and exposure time. Ambient (urban) aerosols showed a very limited capacity to take up N₂O₅ but were reactive towards NO₃ with γ(NO₃)/γ(N₂O₅)>15. A value of γ(NO₃)/γ(N₂O₅)~1.5–3 was obtained when using candle generated soot. The relative rate obtained for Saharan dust can be placed on an absolute basis using our recently determined value of γ(N₂O₅)=1×10⁻² to give γ(NO₃)=9×10⁻³, which is significantly smaller than the single previous value. With the present uptake coefficient, reaction of NO₃ with mineral dust will generally not contribute significantly to its NO₃ loss in the boundary atmosphere or to the nitration of mineral dust.