Heterogeneous Uptake of HO2 Radicals onto Submicron Atmospheric Aerosols

P.S.J. Matthews, I.J. George, B. Brooks, L.K. Whalley, M.T. Baeza Romero, and D.E. Heard.

The HO2 uptake coefficient is an important parameter that needs to be included into atmospheric models. In this work the uptake coefficients of HO2 by different types of aerosols and under different conditions have been measured using a Fluorescence Assay By Gas Expansion (FAGE) detector combined with a flow tube.

It is important to be able to accurately predict HOx (OH and HO2) concentrations as HOx radicals are responsible for the majority of the oxidation in the troposphere and control the concentrations of many trace species in the atmosphere. However, many field measurement studies have reported significantly lower HO2 radical concentrations than calculated by constrained box models using detailed chemical mechanisms. HO2 uptake by aerosols has been suggested as a possible sink in many different environments such as in the MBL (1), the Arctic troposphere (2) and the upper troposphere (3). Although there have been very few laboratory studies (4,5) on HO2 uptake by aerosols, a large range of uptake coefficients (γ= 0.005- 0.9) have been measured and the rates and mechanism are still uncertain.

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