Oxygenated organic molecules (OOMs) from oxidation of volatile organic compounds (VOCs) are important contributors to secondary organic aerosol (SOA) formation. Recent field studies showed that anthropogenic precursors significantly contributed to OOMs and subsequent SOA formation in urban areas. We conducted collocated OOM measurements with nitrate-ion chemical ionization mass spectrometry and SOA molecular tracer measurements with thermal desorption aerosol gas chromatography-mass spectrometry in Shanghai. Using the newly developed OOM-based method, we found that OOMs derived from aromatic VOCs (aromatic OOMs) dominated the local SOA production with a contribution of 52%. The traditional SOA tracer-based method estimated a consistent fraction of 49% from monoaromatics and polyaromatics (e.g., naphthalene and methylnaphthalene). We further categorized the aromatic OOMs into heavy (carbon number: nC > 9) and light (nC = 6-9) ones primarily based on the ring number. Surprisingly, the contribution of heavy aromatic OOMs to SOA formation (25%) was more than twice of the naphthalene-derived SOA from the tracer-based method (10%). The gap could be explained by the fact that the OOM-based method also counted the contributions from other polyaromatic VOCs that are beyond methyl-/naphthalene. The high degrees of oxygenation caused by multistep oxidation and the higher carbon number (nC > 9) in heavy aromatic OOMs lead to their lower volatility and higher contributions to SOA. Our study provides previously unavailable linkage between the aromatic SOA with its precursors via simultaneous measurements of OOMs and molecular tracers, revealing the overlooked contribution from heavy aromatic VOCs to SOA formation.