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

Abstract

Atmospheric hydrogen peroxide (H 2 O 2 ) plays an important role in sulfate formation. To explore the contribution of the H 2 O 2 oxidation pathway to atmospheric sulfate in winter in Beijing, three field campaigns of atmospheric H 2 O 2 measurements were conducted at an urban site (Beijing) and a rural site (Wangdu) during the winter in 2016, 2017, and 2018. The H 2 O 2 concentrations were usually around the detection limit (0.05 ppbv) during clean and severely polluted periods, whereas the highest H 2 O 2 concentration of 0.90 ppbv was observed during moderately polluted periods. Obvious increases in the concentration of H 2 O 2 could be observed after sunset at the urban site during each moderately polluted day, which was mainly attributed to transportation of H 2 O 2 -rich air from the rural areas in the south of Beijing. Coincident increases in the concentrations of H 2 O 2 and PM 2.5 were also observed during the day at high NO concentrations, implying that heterogeneous reactions might contribute to the formation of H 2 O 2 under polluted conditions. In addition, the contrast between urban and rural measurements also provides some support for the potential formation of H 2 O 2 from heterogeneous reactions. On the basis of the data measured in this study, sulfate formation through H 2 O 2 oxidation was found to be the dominant pathway rather than the NO 2 oxidation pathway.

Formation mechanisms of atmospheric nitrate and sulfate during the winter haze pollution periods in Beijing: gas-phase, heterogeneous and aqueous-phase chemistry

“…4, similar to the daily variations in NOR, the mean values of SOR were found to elevate remarkably under the 30 % < RH < 60 % condition compared to the RH ≤ 30 % condition, especially during 14:00-22:00 UTC+8, which might be mainly ascribed to the enhanced gas-phase reaction and the heterogeneous reaction of SO 2 involving aerosol liquid water under the relatively high-RH condition. The extremely high mean values of SOR during the whole day under the RH ≥ 60 % condition implied that aqueous oxidation of SO 2 dominated the formation of sulfate during the severe pollution episodes, which was in line with previous studies (Zhang et al, 2018;Cheng et al, 2016). A key factor that influenced the aqueous oxidation pathways for sulfate formation has been considered to be the aerosol pH (Guo et al, 2017;M.…”

“…Atmospheric sulfate is principally from the SO 2 oxidation pathway, including gas-phase reactions with OH radicals or stabilized Criegee intermediates, heterogeneous-phase reactions on the surface of particles, and aqueous-phase reactions with dissolved O 3 , NO 2 , H 2 O 2 , and organic peroxides, as well as autoxidation catalyzed by TMI Li et al, 2018;Ravishankara, 1997;Shao et al, 2019;Wang et al, 2016;Xue et al, 2016;Zhang et al, 2018). As shown in Fig.…”

Supplementary material to &quot;Partitioning of hydrogen peroxide in gas-liquid and gas-aerosol phases&quot;

“…We calculate the reaction rate (RR) and the sulfate formation rate (SFR) during a heavy haze episode. Given that pH was around 5 in aerosols consistent with recent studies (Liu et al, 2017;Ye et al, 2018), the results are listed in Table S4.…”

RH and O&lt;sub&gt;3&lt;/sub&gt; concentration as two prerequisites for sulfate formation

“…As the O3 oxidation route can be excluded in a heavily polluted area with high aerosol acidity (Shen et al, 2012;Sievering et al, 2004), such as Beijing, the two prerequisites suggest that H2O2 oxidation might be the major sulfate formation route. Such a conclusion is supported by a recent report of model underestimations of 5 H2O2 concentrations in the Beijing area (Ye et al, 2018).…”