Abstract
Abstract. Uptake coefficients for HO2 radicals onto Arizona test dust (ATD) aerosols were measured at room temperature and atmospheric pressure using an aerosol flow tube and the sensitive fluorescence assay by gas expansion (FAGE) technique, enabling HO2 concentrations in the range 3–10 × 108 molecule cm−3 to be investigated. The uptake coefficients were measured as 0.031 ± 0.008 and 0.018 ± 0.006 for the lower and higher HO2 concentrations, respectively, over a range of relative humidities (5–76%). A time dependence for the HO2 uptake onto the ATD aerosols was observed, with larger uptake coefficients observed at shorter reaction times. The combination of time and HO2 concentration dependencies suggest either the partial saturation of the dust surface or that a chemical component of the dust is partially consumed whilst the aerosols are exposed to HO2. A constrained box model is used to show that HO2 uptake to dust surfaces may be an important loss pathway of HO2 in the atmosphere.
Highlights
OH and HO2 radicals, collectively known as HOx, are closely coupled and together are responsible for the majority of the oxidation in the troposphere
The HO2 uptake coefficient on Arizona test dust aerosol was measured as γ = 0.031 ± 0.008 and γ = 0.018±0.006 for initial HO2 concentrations of 3 × 108 and 1 × 109 molecule cm−3, respectively, with very little dependence upon relative humidity observed over a wide range (6–76 %)
The atmospheric impact of the uptake onto dust aerosols on HO2 concentrations was investigated for the conditions encountered at the Cape Verde Atmospheric Observatory in the tropical Atlantic Ocean
Summary
OH and HO2 radicals, collectively known as HOx, are closely coupled and together are responsible for the majority of the oxidation in the troposphere. J. Matthews et al.: Uptake of HO2 radicals onto ATD particles the concentrations of several important species, for example NOx, O3 and HOx (Dentener et al, 1996; Tang et al, 2014). There are currently no studies measuring HO2 uptake coefficients onto ATD aerosols (rather than surfaces) or under atmospherically relevant HO2 concentrations. The aim of this study was to measure the HO2 uptake coefficient for ATD aerosols at two different initial HO2 concentrations (1 × 109 and 3 × 108 molecule cm−3), over a range of relative humidities (6–73 % RH) and as a function of the time that the ATD aerosol particles are exposed to the HO2 radicals
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