Fireworks are a well-known source of barium (Ba) in the atmosphere, yet their aging processes remain poorly understood. Using single-particle aerosol mass spectrometry (SPAMS) in Guangzhou, China, we show that firework events elevated atmospheric Ba concentrations by 1<em>–</em>3 orders of magnitude above background levels. The highest concentrations occurred in restricted zones rather than the more densely populated urban core, demonstrating the effectiveness of local restriction policies. Critically, we identified two distinct mixing states along the aging continuum, chloride-rich OClN particles (containing BaCl<sub>2</sub>) and nitrate-dominated N particles (containing Ba(NO<sub>3</sub>)<sub>2</sub>). This chemical conversion co-occurred with physical coagulation involving Al/Mg-containing particles, which mixed preferentially with OClN over N. Observed lags of several hours between OClN and N peaks and between NO<sub>2</sub> and particulate NO<sub>3</sub><em><sup>–</sup></em> point to nitrate formation as a key aging pathway. These findings elucidate the rapid aging mechanisms of firework-derived Ba particles and provide direct evidence that emission controls effectively mitigate firework pollution.