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With the rapid increase of the vehicle population in the Guanzhong Plain (GZP), the fine particulate matter (PM2.5) emitted by vehicles has an impact on regional air quality and public health. The spatial distribution of primary and secondary PM2.5 concentrations from vehicles in GZP in January and July 2017 was simulated in this study by using the Weather Research and Forecasting (WRF) model and the California Puff (CALPUFF) air quality model. The contributions of vehicle-related emission sources to total PM2.5 concentrations were also calculated. The results show that although the emissions of primary PM2.5, NOx, and SO2 in July were greater than those in January, the hourly average concentrations of primary and secondary PM2.5 in January were significantly higher than those in July. The highest concentrations of primary and total PM2.5 were mostly located in the urban areas of Xi'an and Xianyang in the central region of GZP. The contributions of exhaust emissions, secondary nitrates, brake wear, tire wear, and secondary sulfate to the total PM2.5 concentrations in GZP were 50.37%, 34.76%, 10.79%, 4.06%, and 0.04% in January and 71.91%, 11.14%, 11.89%, 5.03%, and 0.03% in July, respectively. These results will help us to further control PM2.5 pollution caused by vehicles. [ABSTRACT FROM AUTHOR]

Vehicle emissions are affected by factors such as vehicle type, fuel quality, and engine repair. Therefore, mobile source profiles should be established based on a characteristic fleet for a specific region. This study characterised the chemical composition of PM 2.5 emitted from motor vehicles that are commonly used in Xi'an through dynamometer tests. The tested fleet included light duty diesel vehicles (LDDVs; eight sample sets), heavy duty diesel vehicles (HDDVs; six sample sets), light duty gasoline vehicles (LDGVs; eight sample sets), one natural gas vehicle (NGV; four sample sets) and one methanol vehicle (MV; two sample sets). Similarities and differences among the source profiles were compared and evaluated. Overall, carbon species (13.14–59.11%) were the major components of PM 2.5 for each type of vehicle, and the content of organic carbon (OC) was generally higher than that of elemental carbon (EC). Moreover, NO 3 − (18.577–220.062 mg·g−1) was the dominant water-soluble ion and the Ca2+ (2.429–17.209 mg·g−1) and Na+ (1.966–20.798 mg·g−1) contents in PM 2.5 were high. In terms of elements, the PM 2.5 emitted from various types of vehicles consisted of abundant Al (2.183–94.949 mg·g−1), Fe (0.567–12.297 mg·g−1), and Zn (0.659–5.195 mg·g−11). In addition, the PM 2.5 profiles were significantly affected by fuel type. In general, emissions from the LDGVs and NGV exhibited higher contents of OC (477.0–479.1 mg·g−1). The greatest fractions of water-soluble ions (32.94%) and total elements (11.74%) were observed in emissions from the NGV and MV, respectively. For the same type of vehicle, the OC/EC ratio was possibly dependent on the emission standards. The PM 2.5 emitted from the LDDVs with stricter emission standards exhibited higher OC/EC ratios, whereas the OC/EC ratios displayed a decreasing trend for the LDGVs under more stringent emission standards. Unlabelled Image • PM 2.5 profiles of conventional and alternative fuel vehicles were characterised. • Gasoline and natural gas vehicles emitted higher contents of OC. • The highest fraction of water-soluble ions was observed from the NGV. • The highest percentage of elements was observed from the MV. • The OC/EC ratio was impacted by the emission standards for the same type of vehicle. [ABSTRACT FROM AUTHOR]