Intermediate and semi-volatility organic compounds (I/SVOCs) emission from Chinese vehicles: volatility distribution, influencing factors, and implication for SOA formation

Highlights

	● I/SVOCs profile and volatility distributions from vehicles were established.
	● Stricter emission standards reduced organic emissions but increased I/SVOC fraction.
	● Speciation analysis enhanced SOA prediction accuracy compared to GC-MS.

Abstract

Intermediate and semi-volatility organic compounds (I/SVOCs) are crucial precursors for secondary organic aerosols (SOA). Vehicles are major sources of I/SVOCs, yet their emission profiles remain insufficiently characterized. We conducted dynamometer tests on eight in-use gasoline and diesel vehicles (DVs), employing non-targeted analysis with comprehensive two-dimensional gas chromatography coupled with high-resolution mass spectrometry (GC × GC-TOFMS) to investigate vehicular I/SVOC emissions at the molecular level. A total of 438 and 424 compounds were identified and (semi)-quantified in the gas and particle phases, respectively. DVs exhibited higher emission factors (376.7 ± 74.9 mg/(kg·fuel)) compared to gasoline vehicles (GVs) (114.4 ± 42.1 mg/(kg·fuel)) across both phases. Alkanes (29.7%–41.9%), single-ring aromatics (2.6%–29.8%), and cycloalkanes (1.0%–13.1%) were dominant I/SVOCs groups. Oxygenated I/SVOCs were more abundant in particulate phases (40.3%–56.8%) than in gas phases (14.4%–15.3%). Upgrading emission standards reduced organic emissions by 89.2% from China IV to China VI for DVs, particularly in the particle phase. Cold-start conditions resulted in higher I/SVOC emissions (528.4 mg/(kg·fuel)) than hot-starts (224.8 mg/(kg·fuel)) due to reduced combustion efficiency and suboptimal after-treatment performance at low temperatures. Our composition-based SOA estimation method improved SOA predictions by 1.5 and 1.2 times for diesel and GVs, respectively, compared to the traditional bin approach. These findings provide valuable insights into the molecular composition of vehicular I/SVOCs and their environmental impacts.

Graphical abstract

Keywords

Vehicle emissions / Non-targeted analysis / I/SVOCs / Chemical fingerprinting / SOA formation potential

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Conflict of Interests

Jianfei Peng is a youth editorial board member of Frontiers of Environmental Science & Engineering. And the authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgements

This work was financially supported by the National Key Research and Development Program of China (Nos. 2023YFC3706201 and 2022YFE0135000), the National Natural Science Foundation of China (Nos. 42175123 and 42311530112), and the Fundamental Research Funds for the Central Universities of China (Nos. 63241318, 63241322, and 63243126).

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