title: Emission factors of air pollutants from CNG-gasoline bi-fuel vehicles: Part II. CO, HC and NOx.
abstract: The estimation of emission factors (EFs) is the basis of accurate emission inventory. However, the EFs of air pollutants for motor vehicles vary under different operating conditions, which will cause uncertainty in developing emission inventory. Natural gas (NG), considered as a "cleaner" fuel than gasoline, is increasingly being used to reduce combustion emissions. However, information is scarce about how much emission reduction can be achieved by motor vehicles burning NG (NGVs) under real road driving conditions, which is necessary for evaluating the environmental benefits for NGVs. Here, online, in situ measurements of the emissions from nine bi-fuel vehicles were conducted under different operating conditions on the real road. A comparative study was performed for the EFs of black carbon (BC), carbon monoxide (CO), hydrocarbons (HCs) and nitrogen oxides (NOx) for each operating condition when the vehicles using gasoline and compressed NG (CNG) as fuel. BC EFs were reported in part I. The part II in this paper series reports the influence of operating conditions and fuel types on the EFs of CO, HC and NOx. Fuel-based EFs of CO showed good correlations with speed when burning CNG and gasoline. The correlation between fuel-based HC EFs and speed was relatively weak whether burning CNG or gasoline. The fuel-based NOx EFs moderately correlated with speed when burning CNG, but weakly correlated with gasoline. As for HC, the mileage-based EFs of gasoline vehicles are 2.39-12.59 times higher than those of CNG vehicles. The mileage-based NOx EFs of CNG vehicles are slightly higher than those of gasoline vehicles. These results would facilitate a detailed analysis of the environmental benefits for replacing gasoline with CNG in light duty vehicles.
authors.affiliation: Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Canada.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Huang
authors.affiliation: Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen, China; Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Canada.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Xing
authors.affiliation: Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Canada. Electronic address: kddu@ucalgary.ca.
authors.forename: Ke
authors.initials: K
authors.lastname: Du
mesh_terms: D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D002248:Carbon Monoxide / Q000032:analysis; D004784:Environmental Monitoring; D004787:Environmental Pollution / Q000032:analysis / Q000517:prevention & control; D006838:Hydrocarbons / Q000032:analysis; D018986:Motor Vehicles; D059206:Natural Gas; D009589:Nitrogen Oxides / Q000032:analysis; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D006838:Hydrocarbons; D059206:Natural Gas; D009589:Nitrogen Oxides; D001335:Vehicle Emissions; D002248:Carbon Monoxide
keywords: Bi-fuel vehicle; CNG; Emission factors; Motor vehicle emission