Emission Factors of CH₄ and CO₂ Emitted from Vehicles

Abstract

The study of the Emission Factors (EF) of methane (CH₄) and Carbon Dioxide (CO₂) emitted from vehicle exhaust is the study of greenhouse gases that are crucial to climate change. These gases are part of a fuel known as Compressed Natural Gas (CNG) or as Natural Gas for Vehicles (NGV) in Thailand. This fuel is used as an alternative to oil, which has decreased the amount of gasoline and diesel oil used in the transportation sector of Thailand. This study used different types of cars that were tested on a chassis dynamometer with a Bangkok driving cycle to measure the emissions of CH₄ and CO₂ and then to calculate the averages of EF-CH₄ and EF-CO₂, which are associated with speed and fuel consumption, respectively. This study was conducted in 3 vehicle types that are actually used in Thailand, namely, Heavy Duty Diesel Vehicles (HDDV), Light Duty Diesel Vehicles (LDDV) and Light Duty Gasoline Vehicles (LDGV). Our results showed that of the three vehicle types, HDDV produced the highest EF-CH₄ and EF-CO₂ averages at 7.22 and 919.6 g km^-1, respectively. LDDV produced the lowest EF-CH₄ (0.17 g km^-1) and LDGV produced the lowest EF-CO₂ (153.8 g km^-1). In addition, the EF-CH₄ and EF-CO2values of LDDV and LDGV were comparable even though the engine types of these vehicles were different. With respect to fuel consumption, the EF-CH₄ and EF-CO₂ of HDDV indicated a higher fuel consumption, which differed from those of LDDV and LDGV. Nevertheless, LDGV or taxis, which account for a large portion of the transportation sector in Thailand, emitted higher proportions of CH₄ and CO₂ than the other vehicle types, as shown by the CH₄:CO₂ ratio. Therefore, according to the results, the EF-CH₄ and EF-CO₂ values can be applied for the effective evaluation of CH₄ and CO₂ emissions from vehicles in Thailand.