Evaluating Nitrogen Oxides and Ultrafine Particulate Matter Emission Features of Urban Bus Based on Real-World Driving Conditions in the Yangtze River Delta Area, China

A Portable Emission Measurement System was used in this study to evaluate the exhaust emission characteristics of nitrogen oxides (NOx), ultrafine particulate matter (PM), and ultrafine particulate number (PN) from buses in the Yangtze River Delta, China. Results showed that NOx emission factor (unit: g center dot km(-1)) increased from 5.0 to 19.1, and PM emission factor (unit: g center dot km(-1)) increased from 0.001 to 0.189. A nonlinear model was established based on scientific statistical method, which showed that NOx and PM emission factors significantly decreased with speed increasing. The model also showed a long tail effect of NOx and PM emission factors beyond 30 km center dot h(-1). Furthermore, hybrid bus exhausted less NOx, PM, and PN emissions compared to conventional bus in the acceleration condition. Exhaust rates of NOx, PM and PN emissions (unit: g center dot s(-1)) increased with speed increasing under steady state driving condition, while PN emissions commonly showed a unimodal distribution at the speed of 20 km center dot h(-1).