High H₂O₂ Concentrations Observed during Haze Periods during the Winter in Beijing: Importance of H₂O₂ Oxidation in Sulfate Formation

Abstract

Atmospheric hydrogen peroxide (H2O2) plays an important role in sulfate formation. To explore the contribution of the H2O2 oxidation pathway to atmospheric sulfate in winter in Beijing, three field campaigns of atmospheric H2O2 measurements were conducted at an urban site (Beijing) and a rural site (Wangdu) during the winter in 2016, 2017, and 2018. The H2O2 concentrations were usually around the detection limit (0.05 ppbv) during clean and severely polluted periods, whereas the highest H2O2 concentration of 0.90 ppbv was observed during moderately polluted periods. Obvious increases in the concentration of H2O2 could be observed after sunset at the urban site during each moderately polluted day, which was mainly attributed to transportation of H2O2-rich air from the rural areas in the south of Beijing. Coincident increases in the concentrations of H2O2 and PM2.5 were also observed during the day at high NO concentrations, implying that heterogeneous reactions might contribute to the formation of H2O2 under polluted conditions. In addition, the contrast between urban and rural measurements also provides some support for the potential formation of H2O2 from heterogeneous reactions. On the basis of the data measured in this study, sulfate formation through H2O2 oxidation was found to be the dominant pathway rather than the NO2 oxidation pathway.