Influence of aerosol copper on HO2 uptake: a novel parameterized equation

Heterogeneous uptake of hydroperoxyl radicals (HO2) onto aerosols has been proposed to be a significant sink of HOx, hence impacting the atmospheric oxidation capacity. Accurate calculation of the HO2 uptake coefficient gamma(HO2) is key to quantifying the potential impact of this atmospheric process. Laboratory studies show that gamma(HO2) can vary by orders of magnitude due to changes in aerosol properties, especially aerosol soluble copper (Cu) concentration and aerosol liquid water content (ALWC). In this study we present a state-of-the-art model called MARK to simulate both gas- and aerosol-phase chemistry for the uptake of HO2 onto Cu-doped aerosols. Moreover, a novel parameterization of HO2 uptake was developed that considers changes in relative humidity (RH) and condensed-phase Cu ion concentrations and which is based on a model optimization using previously published and new laboratory data included in this work. This new parameterization will be applicable to wet aerosols, and it will complement current IUPAC recommendations. The new parameterization is as follows (the explanations for symbols are in the Appendix): 1/gamma(HO2) = 1/alpha(HO2) + 3x upsilon(HO2)/4 x10(6)xR(d)H(corr)RTx(5.87+3.2xln(ALWC/[PM]+0.067))x[PM](-0.2) x [Cu2+](eff)(0.65) +upsilon(HO2)l/RTHorg D-org epsilon All parameters used in the paper are summarized in Table A1. Using this new equation, field data from a field campaign were used to evaluate the impact of the HO2 up-take onto aerosols on the ROx (= OH + HO2 + RO2) budget. Highly variable values for HO2 uptake were obtained for the North China Plain (median value < 0.1).