Real-World Vehicle Exhaust Emissions Monitoring: Review and Critical Discussion

Traffic-related emissions represent a major component of airborne pollution. Historically, dynamometer testing has been most widely used to estimate vehicle emission rates, and these emission rates, in turn, have been used as inputs when modeling traffic-related air quality impacts. However, such conventional drive cycle testing is not considered strictly representative of vehicles under real driving conditions. Therefore, in recent years, significant scientific effort has been focused on the measurement and analysis of real-world vehicle emissions. Here, the use of vehicle emissions monitoring methods (e.g., in-situ methods such as tunnel, inverse dispersion, and remote sensing studies, and in-traffic measures such as probe vehicle and “car chaser” studies) to provide real-world emission estimates is reviewed and discussed in detail. Advantages and disadvantages are identified for the different vehicle emissions monitoring methods, both relative to dynamometer-based approaches and each other. Potential applications of different approaches are also discussed, with particular attention being placed on their complementary use.