Uptake of NO₃ and N₂O₅ to Saharan dust, ambient urban aerosol and soot: a relative rate study

• Main Authors: J. N. Crowley, G. Schuster, J. Thieser, M. J. Tang
• Format: Article
• Language: English
• Published: Copernicus Publications 2010-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/10/2965/2010/acp-10-2965-2010.pdf

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.