Acid-catalyzed heterogeneous reaction can lead to potentially multifold increase in secondary organic aerosol (SOA) generation, which may have a greater impact on climate forcing effects. In this study, single particle aerosol mass spectrometry (SPAMS) and scanning mobility particle sizer (SMPS) were applied to perform an online study of the chemical and physical characteristics of the pyrene-coated inorganic seed particle ozonation in a smog chamber to examine the influence of seed acidity on pyrene-SOA formation. Acidic seed particles are made of ammonium sulfate, ammonium bisulfate and sulfuric acid in different proportions. F_s, the inorganic seed composition number, is defined as a ratio of the molar concentration of SO₄²⁻ to the total molar concentration of SO₄²⁻ and NH₄⁺ in this study. Suspended pyrene-coated acidic seed particles were generated by the vaporization-condensation method. Homogeneous and heterogeneous reaction products were identified and assigned. The results show that the seed particle acidity can enhance the mass yield, as well as the chemical diversity of pyrene-SOAs, and also dramatically increase the formation of new smaller particles. Kinetic analysis revealed that the first-order reaction rate constant (K) of acidic seed particles was much higher than that of neutral seed particles, with K values for F_s = 0.77 being 1.47 times that of F_s = 0.50 and 2.58 times that of F_s = 0.33. A mechanism for pyrene-SOA formation was also proposed based on real-time monitoring. For neutral seeds, the pyrene ozonation preferred ‘atom attack’ and mainly formed 1-hydroxypyrene; while for acidic seeds, the pyrene ozonation preferred ‘bond attack’ and formed a Criegee intermediate, followed by broken C–O and C–C bonds, thereby resulting in a variety of semi- and low-volatile products. This study presents a rapid analytical method for the combined use of smog chamber, SPAMS, and SMPS to immediately characterize the effect of seed particle acidity on the formation of polycyclic aromatic hydrocarbon SOA, which may deepen our understanding of new particle formation and particle growth in the atmosphere. Therefore, the present study provides a new insight for an in-depth understanding of haze pollution in China.