AbstractIsoprene is a substantial contributor to global secondary organic aerosol (SOA). The formation of isoprene SOA (SOA_I) is highly influenced by anthropogenic emissions. Currently, there is rare information regarding SOA_I in polluted regions. In this study, one-year concurrent observation of SOA_I tracers was undertaken at 12 sites across China for the first time. The tracers formed from the HO₂-channel exhibited higher concentrations at rural sites, while the tracer formed from the NO/NO₂-channel showed higher levels at urban sites. 3-Methyltetrahydrofuran-3,4-diols exhibited linear correlations with their ring-opening products, C₅-alkenetriols. And the slopes were steeper in the southern China than the northern China, indicating stronger ring-opening reactions there. The correlation analysis of SOA_I tracers with the factor determining biogenic emission and the tracer of biomass burning (levoglucosan) implied that the high level of SOA_I during summer was controlled by biogenic emission, while the unexpected increase of SOA_I during winter was largely due to the elevated biomass burning emission. The estimated secondary organic carbon from isoprene (SOC_I) exhibited the highest levels in Southwest China. The significant correlations of SOC_I between paired sites implied the regional impact of SOA_I in China. Our findings implicate that isoprene origins and SOA_I formation are distinctive in polluted regions.