Abstract: Face masks are usually used to prevent inhalable particles and microdroplets that may enter the nose and mouth. However, a lot of organic contaminants can be found in materials, manufacturing processes, or packaging of face mask, so there is a potential health risk during mask-wearing for a long time. Benzaldehyde is one of the simple and common aromatic aldehydes with highly active chemical properties, which is one of the typical contaminants in face mask and is a high-risk volatile organic compound for human health. To understand the potential health risk of benzaldehyde during wearing a mask, it is of great significance to monitor the possible photochemical reaction of benzaldehyde during mask-wearing under the conditions of sunshine and ozone. Mass spectrometry has attracted extensive attention in monitoring chemical reactions under complex environmental conditions, because of its high sensitivity, excellent accuracy and fast signal response. Direct mass spectrometry can provide a powerful tool for sample analysis, which requires no or little sample pretreatment. In this study, the products of benzaldehyde under different treatment conditions were investigated by direct mass spectrometry with direct electrospray ionization on mask material, and were further verified by comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) that can provide a high-resolution separation and highly sensitive detection for complex volatile samples. Photochemical reaction and oxidation reaction mechanisms of benzaldehyde were also proposed. The results showed that many organic compounds such as benzophenone, 4-pentenoic acid, methyl benzoate, benzoic acid can be formed by benzaldehyde under exposure to ultraviolet (UV) light and ozone. This method can provide a new way to gain insight into contaminants of mask devices under different environmental conditions.