EMFAC-HK Web Based Training

Glossary

Activity: An emission inventory is simply a product of the emission rate (in grams per kilometer or grams per trip or grams per vehicle) and vehicle activity (kilometres per vehicle or number of trips or total number of vehicles). This requires estimates of vehicle population, vehicle kilometres travelled and trips for each vehicle class and by fuel type. These terms are commonly referred as vehicle activity.

Burden mode: This mode is used for calculating regional (area-specific) emission inventories. In this mode, the model reports total emissions as tonnes per weekday for each pollutant, by vehicle class and the total vehicle fleet.

Diurnal: HC emissions that occur when rising ambient temperatures cause fuel evaporation from vehicles sitting throughout the day. These losses are from leaks in the fuel system, fuel hoses, and connectors, and as a result of breakthrough of vapours from the carbon canister. If a vehicle is sitting for a period of time, emissions from the first 35 minutes are counted as hot soak and emissions from the remaining period are counted as diurnal emissions, provided that the ambient temperature is increasing during the remaining period.

EMFAC mode: This mode generates emission factors in terms of grams of pollutant emitted per vehicle activity. Emission factor can be in terms of grams per kilometer, grams per hour, or grams per start, depending on the emission process. In the EMFAC mode, an additional input form allows users to customize their output and select specific temperature, relative humidity, and speed values.

Fuel Type: EMFAC-HK currently estimates emissions from petrol, diesel, and liquefied-petroleum gas (LPG) powered vehicles. Table 1 shows the fuels modelled by vehicle class.

Fuel RVP: RVP is the abbreviation for "Reid Vapour Pressure," a measure of petrol volatility, as well as a generic term for petrol (fuel) volatility.  

Hot soak: Evaporative HC emissions that occur immediately after a trip end due to fuel heating and the fact that the engine remains hot for a short time after being switched off. In older, carbureted vehicles, these emissions are attributed to vapour losses from the carburetor float bowl. In newer, fuel-injected vehicles, vapour losses come from leaky fuel injectors or from fuel hoses.

Model year: The EMFAC-HK application contains emission factors and vehicle activity data for model years 1965 through 2040. Within each vehicle class, the model year is represented by a combination of technology groups. For example, a non-catalyst petrol-fuelled technology group (TG-1) and a diesel-fuelled technology group (TG-171) represent the 1965 model year for private cars.

Vehicle Population: Vehicle population is determined through an analysis of the licensed vehicle data. These data are used in developing vehicle age matrices with the year 2010 as the base year for vehicle classes, fuel types, and vehicle ages from 1 to 45. These matrices contain actual population estimates, which are used for backcasting and forecasting of vehicle populations during calendar years 1997 to 2040.

Resting losses: These losses, which occur while the vehicle is sitting, are caused by fuel permeation through rubber and plastic components. Emissions are counted as resting loss emissions if the vehicle has not been operated for 35 minutes and is still stationary, but the ambient temperature is either constant or decreasing.

Running losses: Evaporative HC emissions that occur when hot fuel vapours escape from the fuel system or overwhelm the carbon canister while the vehicle is operating.

Running exhaust: Emissions that come out of the vehicle tailpipe while it is traveling on the road.

Starting exhaust: Tailpipe emissions that occur as a result of starting a vehicle. These emissions are independent of running exhaust emissions and can be thought of as a slug of emissions associated with starting a vehicle. The magnitude of starting exhaust depends on how long the vehicle has been sitting before starting. (Starting emissions are only estimated for petrol- and LPG-fuelled vehicles).

Transportation Control Measures (TCMs): Strategies to reduce transportation-related emissions by reducing vehicle use or improving traffic flow.

Trips: The terms "Number of trips per day" and "Number of starts per day" are the same and can be used interchangeably. Both represent the number of separate trips made per weekday. In EMFAC-HK, the estimates for trips per day for vehicle classes are based on preliminary travel surveys. The model calculates the total number of trips for a given calendar year and vehicle class by summing the product of model year populations and trips per day estimates.

Vehicle class: The model performs separate calculations for each of the 16 classes of vehicles, by fuel usage and each technology group. Each vehicle class contains numerous technology groups, which represent common emission characteristics such as emission standards, technologies, or in-use emissions. The vehicle classes currently modelled are shown in Table 1, along with abbreviations used in the model.

Vehicle fleet: All the motor vehicles being operated on roads in Hong Kong. This fleet as currently modelled is classified into 16 categories, called classes (for example, class 1, private cars). These classes are based on the type of vehicle, but weight class and fuel type (gas, diesel, or electricity) are also taken into account. The number of vehicles in each class is based on an analysis of the Transport Department (TD) registration data. These vary by calendar year and geographic area, so the make-up of the vehicle fleet is dependent on the calendar year and geographic area.

Technology group: The underlying assumption is that each vehicle class can be modelled through the unique behavior of different technology groups. Each technology group represents vehicles that come from the same class, share a particular emission control technology, have similar in-use deterioration rates, and respond the same to repair. A technology group can represent vehicles whose emissions standards are the same or have the same specific equipment installed on them (e.g., multi-port fuel injection, three-way catalyst, adaptive fuel controls, etc.) that makes them emit similarly.

Vehicle kilometres travelled (VKT): Vehicle kilometres travelled (VKT) represents the total distance travelled on a weekday. TD estimates annual VKT based on the traffic data collected in their counting stations. Various government departments, like TD and Planning Department (PlanD), have developed transportation models, which provide output of VKT for certain planning years. In the EMFAC-HK model, VKT is related to vehicle population and vehicle accrual. Vehicle accrual is the total number of kilometres a vehicle accumulates in a year, and varies by vehicle age and based on survey data and is re-adjusted based on TD’s annual VKT. The model also contains hourly distributions of VKT by vehicle class. These distributions are based on data collected from TD’s counting stations.