Heterogeneous loss of HO2 by KCl, synthetic sea salt, and natural seawater aerosol particles

The HO2 uptake to aerosol particles is potentially significant sink for the HO2 radical in the marine atmosphere. To assess the heterogeneous loss of HO2 on marine aerosol particles, we have investigated the uptake coefficients (γ) of HO2 for submicron aerosol particles of KCl, synthetic sea salt, and natural seawater under ambient conditions (760 Torr and 296 ± 2 K) using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. γ values determined for dry and wet aerosols of KCl were 0.02 ± 0.01 and 0.07 ± 0.03 at 66% and 75% RH, respectively, while γ values for those doped with CuSO4 was 0.55 ± 0.19 at 75% RH. γ values determined for synthetic sea-salt particles were 0.07 ± 0.03, 0.12 ± 0.04 and 0.13 ± 0.04 at 35%, 50%, 75% RH, respectively, while γ values for natural seawater particles were 0.10 ± 0.03, 0.11 ± 0.02 and 0.10 ± 0.03 at 35%, 50%, 75% RH, respectively. We recommend a HO2 uptake coefficient in marine areas of 0.1 for modeling and estimated the contribution of heterogeneous loss of HO2 by sea-salt aerosol particles in marine areas using a box model. Our box-model simulations suggested that daytime maximum HO2 concentrations decreased to 87–94% of the values without heterogeneous loss.