The heterogeneous chemical kinetics of N2O5 on CaCO3 and other atmospheric mineral dust surrogates

[摘要] Uptake experiments of N₂O₅ on several mineral dust powder sampleswere carried out under continuous molecular flow conditions at 298±2 K.At [N₂O₅]₀=(4.0±1.0)×10¹¹ cm⁻³ wehave found γ_ss values ranging from (3.5±1.1)×10⁻²for CaCO₃ to (0.20±0.05) for Saharan Dust with γ_ssdecreasing as [N₂O₅]₀ increased. The uptake coefficientsreported in this work are to be regarded as upper limiting values owing tothe fact that they are based on the geometric (projected) surface area ofthe mineral dust sample. We have observed delayed production of HNO₃upon uptake of N₂O₅ for every investigated sample owing tohydrolysis of N₂O₅ with surface-adsorbed H₂O. Arizona TestDust and Kaolinite turned out to be the samples that generated the largestamount of gas phase HNO₃ with respect to N₂O₅ taken up. Incontrast, the yield of HNO₃ for Saharan Dust and CaCO₃ is lower.On CaCO₃ the disappearance of N₂O₅ was also accompanied bythe formation of CO₂. For CaCO₃ sample masses ranging from 0.33 to2.0 g, the yield of CO₂ was approximately 42–50% with respect to the total number of N₂O₅ molecules taken up. The reaction ofN₂O₅ with mineral dust and the subsequent production of gas phaseHNO₃ lead to a decrease in [NO_x] which may have a significanteffect on global ozone.

[学科分类] 大气科学