Organics Substantially Reduce HO2 Uptake onto Aerosols Containing Transition Metal ions

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• 作者：Pascale S. J. Lakey ; Ingrid J. George ; Maria T. Baeza-Romero ; Lisa K. Whalley ; Dwayne E. Heard
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：March 10, 2016
• 年：2016
• 卷：120
• 期：9
• 页码：1421-1430
• 全文大小：460K
• ISSN：1520-5215

文摘

A HO₂ mass accommodation coefficient of α = 0.23 ± 0.07 was measured onto submicron copper(II)-doped ammonium sulfate aerosols at a relative humidity of 60 ± 3%, at 293 ± 2 K and at an initial HO₂ concentration of ∼1 × 10⁹ molecules cm^–3 by using an aerosol flow tube coupled to a sensitive fluorescence assay by gas expansion (FAGE) HO₂ detection system. The effect upon the HO₂ uptake coefficient γ of adding different organic species (malonic acid, citric acid, 1,2-diaminoethane, tartronic acid, ethylenediaminetetraacetic acid (EDTA), and oxalic acid) into the copper(II)-doped aerosols was investigated. The HO₂ uptake coefficient decreased steadily from the mass accommodation value to γ = 0.008 ± 0.009 when EDTA was added in a one-to-one molar ratio with the copper(II) ions, and to γ = 0.003 ± 0.004 when oxalic acid was added into the aerosol in a ten-to-one molar ratio with the copper(II). EDTA binds strongly to copper(II) ions, potentially making them unavailable for catalytic destruction of HO₂, and could also be acting as a surfactant or changing the viscosity of the aerosol. The addition of oxalic acid to the aerosol potentially forms low-volatility copper–oxalate complexes that reduce the uptake of HO₂ either by changing the viscosity of the aerosol or by causing precipitation out of the aerosol forming a coating. It is likely that there is a high enough oxalate to copper(II) ion ratio in many types of atmospheric aerosols to decrease the HO₂ uptake coefficient. No observable change in the HO₂ uptake coefficient was measured when the other organic species (malonic acid, citric acid, 1,2-diaminoethane, and tartronic acid) were added in a ten-to-one molar ratio with the copper(II) ions.