The high altitude in mountainous regions results in lower atmospheric pressure, oxygen concentration and temperature, leading to lower combustion efficiency in motor vehicles. Therefore, there may be differences in carbon dioxide (CO₂), carbon monoxide (CO), and nitrogen oxides (NO_x) emissions characteristics at different altitudes. In this study, a portable emission measurement system was used to investigate the effects of varying elevations on the emission factors of CO₂, CO, and NO_x on diesel and gasoline-powered vehicles at altitudes ranging from 2270 to 4540 m in the Qinghai–Tibet Plateau of China. Additionally, the influencing factors of CO₂, CO, and NO_x emissions were studied. Results showed that the CO₂, CO, and NO_x emission factors for diesel vehicles varied in the range of 161.83–195.54, 0.59–0.77, and 4.61–6.58 g/km; the population means with 90% confidence intervals were 178.54, 0.68, and 5.60 g/km, respectively. For gasoline vehicles, the CO₂, CO, and NO_x emission factors varied in the range of 161.66–181.98, 0.95–1.06, and 0.12–0.25 g/km; the population means with 90% confidence intervals were 171.82, 1.01, and 0.19 g/km, respectively. Overall, the emission factors of diesel vehicles were higher than those of gasoline vehicles, and the emissions increased with increasing altitude. Atmospheric pressure was identified as the primary environmental factor affecting CO₂, CO, and NO_x emissions. As the speed of motor vehicles increased, the emission of CO₂ also increased, while there was a quadratic relationship with acceleration. This study provides a reference and guidance for vehicle pollution control in high-altitude regions.

Research on the driving characteristics of motor vehicles at different altitudes in plateau regions and road emission intensity can provide technical support for energy conservation and emission reduction policies in plateau areas. This paper selects gasoline and diesel vehicles for on-board testing on typical road sections in plateau regions to study the overall driving characteristics of motor vehicles and the driving characteristics at different altitude intervals in plateau areas. The results show that with the increase in altitude, the driving conditions gradually concentrate towards ’high speed, low acceleration.’ The relevant conclusions can further study and analyze the distribution patterns of pollutants in motor vehicle exhaust emissions and road emission intensity.