摘要:

α-Hydroxy hydroperoxides (α-HHPs) are an important class of atmospheric peroxides, yet their atmospheric fate remains poorly characterized due to limited observations and a lack of modeling studies. Here, we selected hydroxymethyl hydroperoxide (HMHP), the simplest α-HHP, as a proxy for detailed investigation. Field observations were conducted in Beijing during summer and winter 2024 to characterize HMHP's atmospheric behavior and its correlations with other species. HMHP exhibits distinct diurnal variations compared to other common peroxides, likely due to its unique formation pathway via alkene ozonolysis. We also found its correlation with PM2.5 and O3 differs between seasons. In summer, the box model simulation significantly overestimated HMHP concentrations when only gas phase loss processes were considered. Adding heterogeneous uptake driven by S(IV) oxidation and Fenton-like reactions on wet aerosols substantially improved model performance. These aerosol-phase processes further contribute to particle growth and aging by forming inorganic and organic components. In winter, applying the summer-improved mechanism led to significant underestimation on HMHP during PM2.5 growth episodes. We propose that the heterogeneous reaction between H2O2 and HCHO—while playing a minor role in summer when aerosols are wet—becomes important in winter when aerosols are dry and reactive surface sites are available. Overall, aerosols play a dual role: they act as a sink for HMHP through uptake on wet aerosols, but as a source through surface reactions on dry aerosols. Based on our simulation, in summer, HMHP is sourced mainly from Criegee intermediates chemistry and lost via heterogeneous uptake (over 50%), whereas in winter, heterogeneous reactions on dry aerosols become an important source, with dry deposition and uptake as the main sinks. Our findings fill a critical gap in previous research on the observation and modeling study of α-HHPs and reveal a close link between these peroxides and particulate matter.

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