Impacts of Diverse Vehicle Emissions on Ozone Levels in Beijing: Insights into Source Apportionment and Formation Mechanism

Beijing, with the highest number of motor vehicles in China, significantly contributes to O3 pollution through substantial NOx and VOC emissions. Understanding the unique impact of different vehicle emissions on O3 levels is crucial for developing targeted strategies against O3 pollution. This study applied the Community Multiscale Air Quality model to comprehensively investigate the impacts of different types of vehicle emissions on O3 levels in various regions of Beijing, providing valuable insights into source apportionment and formation mechanisms. The results revealed that various types of vehicles exhibited different spatial-temporal emission patterns, with medium-heavy duty trucks (HDT) and mini-light passenger vehicles (LDPV) emerging as the primary contributors to NOx (36.1%) and VOCs (57.6%) emissions, respectively. Total vehicle emissions were found to contribute to over 20% of daily maximum 8–h average O3 (MDA8 O3) concentration, ranking as the second largest contributor in Beijing after regional transport. LDPV and medium-large passenger vehicles (MDPV) contributions were mainly concentrated in urban areas reaching 2.6‒3.4 and 4.1‒6.8 ppb, respectively, while the contributions from mini-light duty trucks (LDT) and HDT were mainly concentrated in suburban areas reaching 3.5‒4.8 and 3.7‒6.2 ppb, respectively. Through scenario analysis that excluded specific vehicular emission components, we found removing LDPV emissions led to sustainable decreases in daytime O3 concentration by 0.3‒3.8 ppb. In contrast, removing MDPV emissions significantly increased O3 levels at 08:00 and 20:00 in urban areas with 4.0‒11.8 ppb. Excluding LDT and HDT emissions resulted in notable increases in nocturnal O3 concentrations while decreases during 13:00‒18:00 period. This study offered valuable insights into the implications of vehicle emissions on O3 levels, providing useful information for decision-makers to devise control strategies targeting vehicle management in the future.