We measured sensitive real-time change of low-chlorinated (Cl(1)-Cl(3)) benzenes in gas phase from heated model and real solid samples using the recently developed vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS). Model solid samples that contained activated carbon, potassium chloride, silicon dioxide, and trace metallic compounds (copper, iron, lead, and zinc) were used to simulate fly ash at a municipal solid waste incinerator (MSWI). The concentrations of chlorobenzenes determined by integrating the area for 30 min using VUV-SPI-IT-TOFMS were correlated with gas-phase concentrations analyzed by GC/MS. Real-time changes had characteristic patterns dependent on metal species and compounds. Comparing gas-phase real-time patterns of low-chlorinated benzenes between real and model fly ashes, copper chloride- and oxide-like compounds in real fly ash at the postcombustion zone in a MSWI may play key factors in the formation of low-chlorinated benzenes. Lead and zinc compounds and iron oxide in solid phase did not affect the formation of low-chlorinated benzenes in gas phase. VUV-SPI-IT-TOFMS can be applied to the time-dependent characterization of volatile low-chlorinated benzenes in gas phase in various artificial and environmental processes.