Does interfacial photochemistry play a role in the photolysis of pyruvic acid in water?

Pyruvic acid (PA) exists in fogs, aerosols and clouds. The photochemistry-driven reaction pathways of PA in the aqueous phase are more elusive than the gas phase. The PA photochemical process may occur in the bulk liquid phase and at the air-liquid interface in ambient conditions. We conducted two sample preparation methods to simulate two possible scenarios: the air-liquid interface and the bulk liquid phase under photolysis. Time-of-flight secondary ion mass spectrometer (ToF-SIMS) was used to analyze samples because of its high sensitivity and mass accuracy in surface analysis. Both negative and positive ion mode mass spectra provide complementary information of the products under different reaction conditions. Spectral principal component analysis (PCA) is used to determine similarities and differences among various samples. The air-liquid interface facilitates more radical reactions and form higher molecular weight compounds (HMWCs) more quickly than the bulk liquid phase, which mainly has non-radical reactions such as anhydride reactions and decarboxylation reactions. Our results show that interfacial chemistry plays an important role in atmospheric scenarios. Moreover, different types of secondary organic aerosols (SOAs) are formed, suggesting the strong influence of interfacial photochemistry has on the earth atmosphere.