Vehicle emissions under real driving conditions: investigating the impact of semi-volatile compounds on air quality

Keywords: Air quality, vehicle emissions, semi-volatile organic compounds, chemical composition.

Vehicle emissions significantly affect air quality, particularly through the release of particulate matter (PM), which pose severe health risks such as respiratory and cardiovascular diseases¹. The world health organization (WHO) has updated guidelines to restrict exposure to these pollutants². Traditional emission models often overlook semi-volatile organic compounds (SVOCs) and intermediate-volatility organic compounds (IVOCs), which play crucial roles in forming secondary organic aerosols (SOAs)³. These compounds contribute to the formation of fine particulate matter (PM) and can have significant health implications due to their ability to penetrate deep into the respiratory system⁴.

This study investigates the impact of the emissions coming from various automotive vehicles on air quality, with a specific focus on semi-volatile organic compounds (SVOCs) measured across different real driving conditions, including urban, rural, and highway. A number of advanced on-line analytical instruments were used to gain a detailed understanding on the emitted compounds. The particle concentration and its distribution size, using a TSI EEPS 3090 and the Horiba OBS ONE SPN₂₃ and SPN₁₀, meanwhile the gas phase analysis was carried out using a Horiba FTX. In addition to real-time measurements, a novel collection system was developed to capture tailpipe emissions as a function of vehicle speed. Those various speed conditions dependent emissions, condensed in liquid phase through a cooling process, were subsequently analyzed offline using an UPLC-Orbitrap-MS. The compounds identified were then classified according to their volatility using the Volatility Basis Set (VBS)⁵.

The relationship between the molecular mass of the emitted compounds and their volatility, based on the engine speed during various test drives was established, providing deeper insights into car emissions of SVOCs and IVOCs.

These findings are important for enhancing the accuracy of air quality models and developing targeted strategies to reduce pollution.

References

¹ Hussain M, Madl P, Khan A (2011), Part-I. Health 2(2):51–59.

² World Health Organization (2021), Geneva, World Health Organization.

³ Robinson AL, Donahue NM, Shrivastava MK, Weitkamp EA, Sage AM, Grieshop AP, Lane TE, Pierce JR, Pandis SN (2007), Science 315(5816):1259–1262.

⁴ Sun J, Shen ZX, Zhang T, Kong SF, Zhang HA, Zhang Q, Niu XY, Huang SS, Xu HM, Ho KF, Cao JJ (2022), Environmental International 165:107344.

⁵ Li Y, Pöschl U, Shiraiwa M (2016), Atmospheric Chemistry and Physics 16(6):3327-3344.