Temperature-dependent evaporation emission and gas/particle partitioning drive the seasonal dynamics of primary intermediate-volatility organic compounds

Abstract. Intermediate-volatility organic compounds (IVOCs) serve as crucial precursors to secondary organic aerosol (SOA), yet their seasonal variations remain insufficiently characterized, impeding a comprehensive understanding of their atmospheric processing and impacts on air quality. To capture the seasonal dynamics of primary IVOCs and identify the key drivers governing their variability, four-season field campaigns were conducted at an urban site in Yangtze River Delta region. The total concentration of measured IVOCs was 1228.2 ± 132.7 ng m⁻³ (average ± 95 % confidence interval), dominated by long-chain alkanes. A distinctive summer-maximum and winter-minimum pattern was identified for measured IVOCs, contrasting sharply with typical seasonal trends of most primarily-emitted air pollutants. This pattern was driven by enhanced temperature-dependent evaporative emissions and efficient particle-to-gas partitioning of low-volatility IVOCs during warm seasons. Petroleum-related sources were confirmed as the dominant contributors to the measured IVOCs. Positive matrix factorization (PMF) model further revealed evaporative emissions as the largest contributor (38.9 %), followed by vehicle exhaust (37.7 %), gas/particle partitioning (14.8 %), and industrial emissions (8.6 %). Our findings elucidate the critical roles of temperature-dependent emissions and gas/particle partitioning in shaping the seasonal cycle of IVOCs, and highlight the potentially expanding contribution of evaporative sources to urban IVOC loads under future climate change scenarios.