New Insights into Secondary Organic Aerosol Formation at the Air-Liquid Interface.

Air-liquid interfacial processing of volatile organic compound photooxidation has been suggested as an important source of secondary organic aerosols. However, owing to the lack of techniques for studying the air-liquid interface, the detailed interfacial mechanism remains speculative. To obviate this, we enabled in situ synchrotron-based vacuum ultraviolet single photon ionization mass spectrometry using the system for analysis at the liquid-vacuum interface microreactor to study glyoxal photooxidation at the air-liquid interface. Determination of reaction intermediates and new oxidation products, including polymers and oligomers, by mass spectral analysis and appearance energy measurements has been reported for the first time. Furthermore, an expanded reaction mechanism of photooxidation and free radical induced reactions as a source of aqueous secondary organic aerosol formation is proposed. Single photon ionization can provide new insights into interfacial chemistry.