Gaseous and Particle Products Formation from α-Pinene Ozonolysis under Conditions of Different Relative Humidities and Particle Seeds

α-Pinene is one of the most important volatile organic compounds (VOCs) emitted from human and biogenic activities. With the increasing ozone concentration in the atmosphere, the α-pinene ozonolysis would enhance atmospheric particle formation by producing gaseous products and secondary organic aerosol (SOA) directly. This study investigated the atmospheric chemistry of α-pinene ozonolysis, focusing on the formation of gaseous and aerosol products under varying relative humidity (RH) and particle seed conditions. Gaseous products were analyzed using PTR-TOF-MS, identifying key compounds such as HCHO, acetone, OH radical, α-pinene oxide, and macromolecular products, with yields of 20.0 ± 3.3% for HCHO and 12.6 ± 2.7% for acetone, 4 ± 2% for α-pinene oxide, and 89.1 ± 10.5% for OH radical. The O/C and H/C ratios of oxidation products remained stable across different conditions, while pinonaldehyde formation was significantly influenced by RH. This study also examined the impact of OH scavengers, particle seeds, and RH on SOA formation. Combining the literature, we figured out that the SOA formation from α-pinene ozonolysis was governed by the multifaceted interdependencies among these variables. Overall, the research emphasizes the significant roles of seeds and humidity in the formation of gaseous products and SOA from α-pinene ozonolysis, contributing to our understanding of atmospheric chemistry.