the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Aug 2026
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.
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Status: open (until 21 Sep 2026)
- RC1: 'Comment on egusphere-2026-4389', Anonymous Referee #1, 21 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-4389', Anonymous Referee #2, 20 Sep 2026
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This manuscript presents a four-season field investigation of primary IVOCs at an urban site in the Yangtze River Delta and explores the roles of temperature-dependent evaporative emissions and gas/particle partitioning in regulating their seasonal variability. The dataset is valuable, and the observed summer-maximum pattern provides useful insights into the atmospheric behavior of IVOCs. The manuscript is generally well organized and suitable for publication after minor revision. I have several comments that may help improve the clarity and robustness of the manuscript.
- Lines 94–108: The field campaigns covered only approximately one week in each season (April 21–27, July 4–10, October 9–15, and December 14–20). Although this design provides observations across four seasons, short-term meteorological episodes may influence the apparent seasonal differences. The authors are encouraged to briefly discuss the representativeness of these sampling periods. For example, were the temperature, PM₂.₅, and other meteorological conditions during each campaign generally representative of the corresponding seasonal conditions? This limitation should also be acknowledged when interpreting the seasonal patterns.
- Lines 260–289: The authors attribute the very low gaseous concentrations of nC₁₉–nC₂₂ in winter and their negative relationship with PM₂.₅ primarily to gas/particle partitioning. This interpretation is reasonable given their relatively low volatility. However, PM₂.₅ concentrations can covary with temperature, boundary-layer dynamics, emission intensity, and other meteorological factors. Therefore, statements such as “a direct consequence” of gas/particle partitioning appear somewhat strong based solely on the observed correlations. The authors are encouraged either to provide additional supporting evidence or to moderate the causal language and briefly discuss possible confounding factors.
- Lines 290–324:Both evaporative emissions and gas/particle partitioning are interpreted as strongly temperature-dependent processes, particularly for the lower-volatility IVOCs. Therefore, it would be helpful if the authors could clarify how the relative roles of these two processes were distinguished based on the current observational dataset. In particular, the authors should explain more explicitly which observational evidence supports enhanced primary evaporative emissions versus particle-to-gas repartitioning. This clarification would strengthen the proposed “temperature–volatility dual-control framework.”
- Lines 349–378: The interpretation of Factor 3 as “gas/particle partitioning” deserves further clarification. Unlike vehicle exhaust, evaporative emissions, and industrial emissions, gas/particle partitioning is an atmospheric process rather than an emission source. The manuscript itself acknowledges that this factor “did not represent a conventional primary emission source.” The authors should therefore explain more clearly how PMF can quantitatively separate this process from temperature-dependent evaporative emissions and why the resulting 14.8% can be interpreted alongside conventional source contributions. It may also be more appropriate to consistently refer to the PMF results as “contributors” rather than “sources”when this factor is included.
- Lines 383–397: The assignment of Factor 2 to evaporative emissions is supported by high loadings of Pr and Ph, low levels of combustion tracers, correlation with isopentane, and temperature dependence. However, evaporative emissions can originate from multiple sources, including fuel evaporation, asphalt, and volatile chemical products, as subsequently discussed by the authors. Therefore, the authors are encouraged to clarify whether the PMF factor specifically represents petroleum/fuel evaporationor a broader category of temperature-dependent evaporative sources. Consistent terminology throughout the manuscript would avoid overinterpretation of this factor.
- Lines 452–468: The authors appropriately note that industrial emissions may contain substantial oxygenated IVOCs that were not included in the current measurements. Since the study targets only 16 representative compounds, mainly hydrocarbon IVOCs, the derived concentrations and PMF contributions may not represent the entire atmospheric IVOC pool. I suggest that the authors more explicitly acknowledge this limitation and consistently use terms such as “measured IVOCs”or “targeted IVOCs”, particularly when discussing source contributions and broader implications.
Citation: https://doi.org/10.5194/egusphere-2026-4389-RC2
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General comments:
This study conducted a four‑season field campaign at an urban site in the Yangtze River Delta, revealing a distinctive seasonal pattern of measured IVOCs, with a maximum in summer and a minimum in winter. The authors provide robust observational evidence that temperature‑dependent evaporative emissions and gas/particle partitioning are the key drivers, and these findings have important implications for SOA modelling and the refinement of emission inventories. Overall, the manuscript is logically structured, and the dataset quality and analytical methodology adopted throughout the study are reliable. I suggest the paper be accepted for publication in ACP pending minor revisions.
Specific comments: