A Novel Insight into the Ozone-Skin Lipid Oxidation Products Observed by Secondary Electrospray Ionization High-Resolution Mass Spectrometry

Emissions of secondary products through reactions of oxidants, ozone (O-3), and hydroxyl radical (center dot OH) with human skin lipids have become increasingly important in indoor environments. Here, we evaluate the secondary organic compounds formed through heterogeneous reactions of gaseous O-3 with hand skin lipids by using a high-resolution quadrupole Orbitrap mass spectrometer coupled to a commercial secondary electrospray ionization (SESI) source. More than 600 ions were detected over a period of less than 40 min realtime measurements, among which 53 ions were characterized with a significant increasing trend in signal intensity at the presence of O-3. Based on the detected ions, we suggest detailed reaction pathways initiated by ozone oxidation of squalene that results in primary and secondary ozonides; we noticed for the first time that these products may be further cleaved by direct reaction of nucleophilic ammonia (NH3), emitted from human skin. Finally, we estimate the fate of secondarily formed carbonyl compounds with respect to their gas-phase reactions with center dot OH, O-3, and NO3 and compared with their removal by air exchange rate (AER) with outdoors. The obtained results suggest that human presence is a source of an important number of organic compounds, which can significantly influence the air quality in indoor environments.