Oxygenated volatile organic compounds (VOCs) as significant but varied contributors to VOC emissions from vehicles

Abstract

Abstract. Vehicular emissions are an important source for volatile organic compounds (VOCs) in urban and downwind regions. In this study, we conducted a chassis dynamometer study to investigate VOC emissions from vehicles using gasoline, diesel, and liquefied petroleum gas (LPG) as fuel. Time-resolved VOC emissions from vehicles are chemically characterized by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) with high frequency. Our results show that emission factors of VOCs generally decrease with the improvement of emission standards for gasoline vehicles, whereas variations in emission factors for diesel vehicles with emission standards are more diverse. Mass spectrum analysis of the PTR-ToF-MS suggests that cold starts significantly influence VOC emissions of gasoline vehicles, while the influences are less important for diesel vehicles. Large differences in VOC emissions between gasoline and diesel vehicles are observed with emission factors of most VOC species from diesel vehicles being higher than gasoline vehicles, especially for most oxygenated volatile organic compounds (OVOCs) and heavier aromatics. These results indicate quantification of heavier species by the PTR-ToF-MS may be important in the characterization of vehicular exhausts. Our results suggest that VOC pairs (e.g., C14 aromatics / toluene ratio) could potentially provide good indicators for distinguishing emissions from gasoline and diesel vehicles. The fractions of OVOCs in total VOC emissions are determined by combining measurements of hydrocarbons from canisters and online observations of the PTR-ToF-MS. We show that OVOCs contribute 9.4 % ± 5.6 % of total VOC emissions for gasoline vehicles, while the fractions are significantly higher for diesel vehicles (52 %–71 %), highlighting the importance of detecting these OVOC species in diesel emissions. Our study demonstrated that the large number of OVOC species measured by the PTR-ToF-MS are important in the characterization of VOC emissions from vehicles.

Online measurements of cycloalkanes based on NO+ chemical ionization in proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS)

“…NO + PTR-ToF-MS was also applied to measure cycloalkane emissions along with other organic compounds from vehicles using gasoline, diesel, and liquified petroleum gas (LPG) as fuel, by conducting a chassis dynamometer measurement (Wang et al, 2022b). Figure 7 shows the time series of C 12 cyclic and bicyclic alkanes, C 12 alkanes, toluene, and acetaldehyde measured by NO + PTR-ToF-MS for a gasoline vehicle with emission standard of China III and a diesel vehicle with emission standard of China IV.…”

“…For instance, the determined emission factors of C 12 cyclic alkanes are 0.06 mg km −1 for gasoline vehicles and 1.17 mg km −1 for diesel vehicles. In addition to cycloalkanes and alkanes, other compounds including aromatics and oxygenated VOCs also demonstrate large differences between gasoline and diesel vehicles, which were mainly attributed to different chemical compositions of gasoline and diesel fuels (Wang et al, 2022b). Recent studies reported that cyclic compounds occupied a large proportion of IVOCs emitted from vehicles, with prominent SOA formation potentials (Fang et al, 2021;Huang et al, 2018;Zhao et al, 2016), but emissions of individual cycloalkanes have not been not reported yet.…”

“…For the species not in the gas standard, we also take advantage of vehicular emissions measurements associated with high concentrations of cycloalkanes, and the sampling methods are the same as mentioned in T Li et al (2021). andWang et al (2022b). Here, we use the delay time to determine response of cycloalkanes, which is calculated based on the time it takes for signals to drop to 10 % of their initial value (Fig.S12)(Pagonis et al, 2017).…”

Experimental and theoretical study of Criegee intermediate (CH2OO) reactions with n-butyraldehyde and isobutyraldehyde: kinetics, implications and atmospheric fate

“…The primary sources for the aldehydes are anthropogenic (mostly from vehicular emission) and biogenic (mainly from vegetation), whereas the secondary sources include the photochemical reactions of VOCs emitted from man-made and natural activities. [41][42][43][44][45] Besides OH radicals, Cl atoms and NO 3 , CH 2 OO was found to have considerably larger rate coefficients with aldehydes. For example, the rate coefficient obtained for the CH 2 OO + CH 3 CHO reaction was (9.5 AE 0.7) Â 10 À13 cm 3 molecule À1 s À1 at 298 K and 4 torr by direct kinetic measurement using photoionization mass spectrometry (PIMS) by Taatjes et al, 31 but it was reported to be (1.48 AE 0.04) Â 10 À12 cm 3 molecule À1 s À1 at 295 K and 25 torr by indirect measurement of the CH 2 OO concentration by Stone et al 13 Similar results were obtained in other studies by Berndt et al 46 and Elsamra et al 47 The reaction mechanism predicted for the CH 2 OO with acetaldehyde is the formation of a secondary ozonide (SOZ), which undergoes 1,5-internal Htransfers from either of the carbon atoms to form hydroxyethyl formate (HEF) and hydroxymethyl acetate (HMA).…”

Manipulation of Waste-Activated Carbon Absorbers as Efficient Carbocatalysts for H2S Selective Oxidation

“…Except for molecules with negligible photochemical reactivity, volatile organic compounds (VOCs) are carbon compounds that engage in atmospheric photochemical processes. , Most of them are highly poisonous, carcinogenic, and dangerous, which bring significant destruction to the nature environment. Styrene (C 8 H 8 ) is a representative aromatic hydrocarbon among the VOCs.…”