Understanding the impact of vehicular emissions on air pollution from the perspective of regional transport: A case study of the Beijing-Tianjin-Hebei region in China

Abstract Motor vehicles are recognised as important contributors to urban air pollution. However, few studies have focused on their contribution from the point of view of regional transport. To address this gap, the validated WRF-CAMx-PSAT modelling system was applied to quantitatively evaluate the impact of vehicular emissions on air pollution in the Beijing-Tianjin-Hebei (BTH) region of China in 2014. We found that although motor vehicle is a near-surface source, it can significantly influence the air quality through regional transmission, especially with respect to atmospheric PM2.5 and NO3− during haze days. The fraction of non-local emissions to the overall vehicular emission contribution was 45.2% and 60.3% for PM2.5 and NO3−, respectively. Furthermore, the regional transport of vehicular emissions played an increased significant role in contributing toward air pollution on haze days. The contribution of non-local vehicular emissions to atmospheric PM2.5 and NO3− from non-haze to haze days increased by 38% and 27%, respectively. An 8.01 times change in the per unit (104 ton) vehicular emission contribution (PVEC) of non-local emissions from non-haze to haze days for NO3− indicated that the control of non-local vehicular emissions can be more effective for the mitigation of NO3− pollution, as compared to the mitigation of undifferentiated emissions from different sources. An obvious power function relationship was found between the PVEC and transport distance. Attenuation index was defined to analyse the degree of attenuation of pollutants with distance. An obvious decrease in the attenuation coefficient from non-haze to haze days for NO3− indicated that the regional transport of NO3− was more prominent on haze days from vehicular emission. Thus, this study can provide new knowledge for understanding the environmental impact of vehicular emissions. In addition, the results can provide a scientific basis for formulating effective regional coordination control strategies for air pollution.