Dark air–liquid interfacial chemistry of glyoxal and hydrogen peroxide

The air–liquid (a–l) interfacial chemistry of glyoxal is of great interest in atmospheric chemistry. We present molecular imaging of glyoxal and hydrogen peroxide (H2O2) dark aging using in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS). More organic peroxides and cluster ions are observed at the a–l interface in dark aging compared to UV aging. Cluster ions formed with more water molecules in dark aging indicate that the aqueous secondary organic aerosol (aqSOA) could form hydrogen bond with water molecules, suggesting that aqSOAs at the aqueous phase are more hydrophilic. Thus the interfacial aqSOA in dark aging could increase hygroscopic growth. Strong contribution of cluster ions and large water clusters in dark aging indicates change of solvation shells at the a–l interface. The observation of organic peroxides and cluster ions indicates that the aqueous surface could be a reservoir of organic peroxides and odd hydrogen radicals at night. Our findings provide new understandings of glyoxal a–l interfacial chemistry and fill in the gap between field measurements and the climate model simulation of aqSOAs. Aerosol particles can act as nuclei for water to condensate and form clouds, which can in turn affect solar radiation budgets. However, aerosol growth and atmospheric reactions during the night-time remain poorly understood due to the current lack of direct observations. Here, Fei Zhang and colleagues present in situ molecular images of organic peroxides and cluster ions which form as secondary aerosols at the air-liquid interface of water droplets (such as those in clouds) during dark, night-time conditions. They find that, in the absence of day-time levels of UV radiation, cluster ions form with more water molecules at night and can therefore absorb more moisture from the air. They suggest that such aqueous surfaces could be a reservoir of organic peroxides and trace hydrogen radicals during the night, and should be incorporated in future atmospheric and climate simulations.