Carbonaceous composition of PM2.5 emitted from on-road China III diesel trucks in Beijing, China

Abstract

Fine particulate matter (PM2.5) has attracted increasing attention due to its impacts on air quality and human health. As an important source of PM2.5, diesel vehicles are often the focus of research. In this study, we characterized the carbonaceous composition of PM2.5 that is emitted from on-road China III diesel trucks (DTs). Organic carbon (OC), elemental carbon (EC), and PM2.5 emission characteristics were determined for 17 China III DTs, including 6 light-duty diesel trucks (LDDTs), 5 medium-duty diesel trucks (MDDTs), and 6 heavy-duty diesel trucks (HDDTs), based on real-world measurements in Beijing, China, using a portable emissions measurement system (PEMS). The average distance-based PM2.5 emission factors (EFs) (g km−1) generally increased and the average CO2-based PM2.5 EFs (g (kg of CO2)−1) generally decreased with increased vehicle size from LDDTs to MDDTs to HDDTs. The effects of driving conditions on the EFs for carbonaceous PM2.5 were analyzed. The results show that distance-based and CO2-based EFs strongly depend on driving conditions. Generally, greater amounts of PM2.5 and OC are emitted from non-highway driving cycles, and greater amounts of EC are emitted from highway driving cycles for vehicles of the same size. For LDDTs, MDDTs, and HDDTs, no significant differences were observed between vehicles with different EC/OC ratios; therefore, the EC/OC ratio is not useful for distinguishing between the emissions generated by differently sized vehicles. The EC/OC, OC/PM2.5, and EC/PM2.5 mass ratios are strongly dependent on driving conditions for vehicles of the same size. The results of this study provide EFs for the carbonaceous composition of PM2.5 that are more appropriate for China; these results will be helpful for improving policies that are designed to control the carbonaceous composition of PM2.5 emitted from on-road DTs in China.