Abstract: On-road emission characteristics of urban vehicles were measured using a portable emission measurement system (PEMS). On-road carbon monoxide (CO), total hydrocarbon (THC), nitrogen oxide (NOx) and particulate matter (PM) emissions were measured. The vehicles included complying with ChinaⅢ,Ⅳemission standards, diesel buses, compressed natural gas (CNG) buses and gasoline taxies with the displacement of 1.6 L complying with ChinaⅢ,Ⅳemission standards. The pollutant emissions of taxies were tested under hot-start and cold-start conditions on chassis dynamometer in laboratory. The impacts of air conditioning on emissions of the buses were researched. Results show that the pollutant emissions levels of the tested taxies under real-world driving conditions are obviously higher than that under the certification cycle conditions; compared to diesel buses, the NOx and THC emission factors of CNG buses are lower, but the PM emission factors may be higher; the use of air conditioning results in serious deterioration of emissions of buses.

Key words: urban vehicles, portable emission measurement system (PEMS), compressed natural gas (CNG) buses, exhaust emission