Measurements of HO2 uptake coefficient on aqueous (NH4)2SO4 aerosol using aerosol flow tube with LIF system

Laboratory studies of HO2 uptake coefficients, γ(HO2), were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence (LIF) system. The measurement was conducted with atmospherically relevant HO2 concentrations (∼1 × 109 molecule/cm3) at 51% RH. The measured γ(HO2) onto aqueous (NH4)2SO4 aerosol was 0.001 ± 0.0007, which was consistent with the relatively low first-order loss rate of HO2 onto aqueous (NH4)2SO4 aerosol. The γ(HO2) was elevated with increase of Cu(II) concentrations in aqueous (NH4)2SO4 aerosol. The threshold of Cu(II) concentration was 10−3 mol/L for the dramatic increase of γ(HO2). It was found that γ(HO2) reached 0.1 when Cu(II) concentration in aerosol was larger than 10−3 mol/L, suggesting that γ(HO2) is very sensitive to concentration of transition metal ions in aerosol.