Uptake of NOsub3/sub and Nsub2/subOsub5/sub to Saharan dust, ambient urban aerosol and soot: a relative rate study

摘要

The uptake of NO₃ and N₂O₅ to Saharan dust, ambient aerosolsand soot was investigated using a novel and simple relative rate method withsimultaneous detection of both NO₃ and N₂O₅. The use ofcavity ring down spectroscopy to detect both trace gases enabled themeasurements 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 orN₂O₅ mixing ratio and exposure time. Ambient (urban) aerosolsshowed a very limited capacity to take up N₂O₅ but were reactivetowards 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 obtainedfor Saharan dust can be placed on an absolute basis using our recentlydetermined value of γ(N₂O₅)=1×10−2 togive γ(NO₃)=9×10−3, which is significantlysmaller than the single previous value. With the present uptake coefficient,reaction of NO₃ with mineral dust will generally not contributesignificantly to its NO₃ loss in the boundary atmosphere or to thenitration of mineral dust.