Regulations on vehicle emission coefficients in Vietnam

In the context of rapid urbanization and economic development, transportation has become one of the main sources of greenhouse gas emissions and pollutants, significantly affecting air quality and human health. To control and minimize this impact, accurate assessment of emissions is essential. One of the most important tools used by scientists and environmental managers is vehicle emission factor.

So, what is the emission factor and how is it calculated? The following article by GREEN IN will help you learn the concept, calculation formula and related regulations in Vietnam, to have the most comprehensive and comprehensive overview of this issue.

What is the vehicle emission factor?

Emission factor (EF) of a vehicle is a technical parameter that expresses the amount of greenhouse gases or other pollutants (NOx​, PM,...) produced per specific unit of vehicle operation. These units can be very diverse, from per liter of fuel consumed, per kilogram of fuel, to per kilometer traveled, or even per engine start.

Determining EF requires relying on scientific research and actual measurement data from a variety of reputable sources. Global organizations such as the Intergovernmental Panel on Climate Change (IPCC) provide scientific emission factors. National and regional environmental agencies such as the European Environment Agency (EEA) and the US Environmental Protection Agency (EPA) also issue specialized guidelines and data sets to support inventories.

Basic emission factor calculation formula

To estimate the emission of a pollutant, experts use a basic formula, specifically the emission level of pollutant (i) due to the use of fuel type (j) (Eij​) is determined as follows:

Eij​=FCj​×EFij​

In which:

• Eij​: Emissions of pollutant (i) when consuming fuel (j) (unit: g).
• FCj​: Mass of fuel consumed (j) (unit: kg).
• EFij​: Emission factor of pollutant (i) per unit of fuel (j) (unit: g/kg fuel or g/km).

This formula serves as the foundation for every emissions inventory report, converting traffic activity data into concrete pollution numbers.

Classification and application of vehicle emission factors

Emission factors are a useful tool for estimating the level of pollution from a particular source and are widely used in emission inventories. The importance of EF is reflected in the following aspects:

• Environmental impact assessment: Helps assess the impact of transport on the environment and human health, thereby determining priority for control measures.
• Strategy Building: Is an important basis for developing and implementing strategies to reduce greenhouse gas emissions and air pollution.
• Management and planning support: Improve the accuracy of emission models, serving effective traffic management and planning.

In engine and emissions studies, EF is often classified based on the unit of measurement, including:

• Base Emission Factor per Engine Power Unit (BSEF): Units are g/kWh, commonly used to calculate the mass of pollutants emitted per engine power.
• Fuel-Based Emission Factor (FBEF): Units are g/kg-fuel, which eliminates the influence of vehicle characteristics and facilitates emissions inventory.
• Distance Based Emission Factor (DBEF): The unit is g/km, which is more suitable and easier to apply in overall inventory activities.

Factors affecting vehicle emission factors

The vehicle emission factor is not a fixed number but depends on many complex factors, including:

• Fuel type and quality: Different fuels (gasoline, diesel, biofuels) will have different chemical compositions, which will produce different combustion products and levels of pollution.
• Technology and operating mode: Engine type, manufacturing technology, and operating method (e.g., speed, sudden acceleration/deceleration) all directly affect combustion efficiency and emission levels.
• Vehicle age and maintenance status: Older vehicles, or vehicles that are not regularly maintained, often have higher emission factors due to engine deterioration and less effective emission control components.
• Pollution control technology: Technologies such as particulate filters (DPFs) or catalytic converters play an important role in reducing pollution, and their presence will significantly reduce EF.
• Actual conditions: External factors such as road conditions, terrain, weather conditions or traffic density can also affect actual emissions results.

Regulations and criteria for selecting emission factors in Vietnam

To ensure effective air quality management, regulations and inventory methods in Vietnam have been clearly established. The establishment of Air Quality Management Plans in provinces and centrally run cities must comply with Law on Environmental Protection 2020 and Decision 985a/QD-TTg.

Emission inventories can be carried out using a top-down, bottom-up, or a combination of both approaches. For transport, the basic formula Eij​=FCj​×EFij​ is applied in detail. References for emission factors are taken from the literature. EMEP/EEA of the European Environment Agency or studies published in Vietnam.

The selection of appropriate emission coefficients for road vehicles in Vietnam follows the main principles:

• Complies with Euro standards: Focus on the Euro emission standards that are being applied, such as Euro 3 for motorcycles and Euro 4 for cars from 1/1/2017.
• Prioritize friendly fuels: Emission factor selection for biofuels (E5, E10, B5), gas fuels (CNG), and hybrid technology.
• Unit of measurement: Prioritize EF values ​​in units of energy used (kg/liter, kg/toe, kg/kWh) for ease of calculation.
• Suitable for Vietnam conditions: Ensure that the selected criteria are appropriate to the country's geographical, climatic and transport infrastructure characteristics.

Research status of vehicle emission coefficient in Vietnam

Research on the development of emission factors for road vehicles in Vietnam is still quite scarce. Many studies have used simulation methods with IVE model (International Vehicle Emission) instead of actual testing. However, some domestic studies have published emission factors based on actual testing and adjusted according to available data, especially for motorcycles and light vehicles in Hanoi.

A representative study developed National Specific Emission Factors (CSEFs) for buses in Hanoi. This study showed that most of the emission factors determined based on the actual operating cycle (HBSC - Hanoi Bus Stationary Cycle) were higher than the values ​​based on the ECE R49 standard cycle. This highlights the importance of using local specific emission factors, as operating characteristics and actual conditions greatly influence the emission results.

Below are some reference figures for vehicle emissions, calculated by distance traveled (g/km):

Conclusion

Vehicle emission factor It is not only a technical parameter but also an important strategic tool for air pollution control and environmental management. Understanding the concepts, classifications and influencing factors will help you to develop more effective policies and action plans.

The current situation in Vietnam shows the need to develop specific emission factors that are suitable for the conditions and operational reality in the country. Only with accurate and reliable data can authorities come up with sustainable solutions to minimize the negative impacts of transportation on the environment and community life.