Impacts of aerosols on the chemistry of atmospheric trace gases: a case study of peroxides and HO2 radicals

H. Liang, Z. M. Chen, D. Huang, Y. Zhao, Z. Y. Li
2013 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> Field measurements of atmospheric peroxides were obtained during the summer on two consecutive years over urban Beijing, which highlighted the impacts of aerosols on the chemistry of peroxide compounds and hydroperoxyl radicals (HO<sub>2</sub>). The major peroxides were determined to be hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), methyl hydroperoxide (MHP), and peroxyacetic acid (PAA). A negative correlation was found between H<sub>2</sub>O<sub>2</sub> and PAA
more » ... n rainwater, providing evidence for a conversion between H<sub>2</sub>O<sub>2</sub> and PAA in the aqueous phase. A standard gas phase chemistry model based on the NCAR Master Mechanism provided a good reproduction of the observed H<sub>2</sub>O<sub>2</sub> profile on non-haze days but greatly overpredicted the H<sub>2</sub>O<sub>2</sub> level on haze days. We attribute this overprediction to the reactive uptake of HO<sub>2</sub> by the aerosols, since there was greatly enhanced aerosol loading and aerosol liquid water content on haze days. The discrepancy between the observed and modeled H<sub>2</sub>O<sub>2</sub> can be diminished by adding to the model a newly proposed transition metal ion catalytic mechanism of HO<sub>2</sub> in aqueous aerosols. This confirms the importance of the aerosol uptake of HO<sub>2</sub> and the subsequent aqueous phase reactions in the reduction of H<sub>2</sub>O<sub>2</sub>. The closure of HO<sub>2</sub> and H<sub>2</sub>O<sub>2</sub> between the gas and aerosol phases suggests that the aerosols do not have a net reactive uptake of H<sub>2</sub>O<sub>2</sub>, because the conversion of HO<sub>2</sub> to H<sub>2</sub>O<sub>2</sub> on aerosols compensates for the H<sub>2</sub>O<sub>2</sub> loss. Laboratory studies for the aerosol uptake of H<sub>2</sub>O<sub>2</sub> in the presence of HO<sub>2</sub> are urgently required to better understand the aerosol uptake of H<sub>2</sub>O<sub>2</sub> in the real atmosphere.</p>
doi:10.5194/acp-13-11259-2013 fatcat:zeieo5caprd6xcnrcsxxz4pznq