IN REAL-WORLD TRAFFIC CONDITIONS OF HANOI
TA HUONG THU, LE ANH TUAN, NGHIEM TRUNG DUNG
Hanoi University of Technology
According to National State of Environment 2007 (Ministry of Natural Resources and Environment), the traffic activities caused 85% CO and 95% VOCs of total emissions in the whole country. Hanoi, with 1.8 millions motorcycles (until June 2007), is now facing with serious air pollution problem . Estimating emission factors of vehicles to calculate total emissions and to serve emission inventories, has great significance for air quality management. In developed countries, by fully worked-out data system of traffic conditions as well as vehicular types, not only emission factors databank, but also statistics about vehicles, has been developed completely through main methods such as: totaling up the numbers of vehicles and experimenting with specific types of vehicles on test beds following given driving cycles; building emission models; or on-road data-based measuring… While doing emission inventories in Hanoi, authorities taking responsibility for management and environmental experts have met a lot of difficulties due to the lack of database. For the exhaust from motorcycles, research about emission factors is in a deep shortage. Until now, researchers only focus on referring emission factors from other countries (e.g. emission factors of USEPA). Specific data are not available at this moment because there has not been any reliable measurement about different vehicular types. The fact shows that, along with the break out of the number of motorcycles in Hanoi, it is very necessary and pressing to set up a set of emission factors for motorcycles. This set needs to be specific for real-world traffic conditions of the city. Due to the limit of time and expenditure, research scope is narrowed into old area of Hanoi (before expanding on August 1st 2008). It also focuses on estimating emission factors of four selected air pollutants of motorcycles: HC (hydrocarbons), CO (carbon monoxide), CO2 (carbon dioxide) and NOx (nitrogen oxides).
II. EMISSION FACTORS AND APPROACHES TO ESTIMATING VEHICULAR EMISSION FACTORS 2.1. Concept
According to USEPA: An emission factor is a tool that is used to estimate air pollution emissions to the atmosphere. It relates the quantity of pollutants released from a source to some activity associated with those emissions. Emission factors are usually expressed as the weight of pollutant emitted divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant. In most cases, these emission factors are simply averages of available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category . Especially for motorcycles (and other mechanical vehicles), emission factors are expressed as grams of pollutant per traveling kilometer or grams of pollutant per liter fuel consumed. 2.2. Methods used to estimate vehicular emission factors  - Fuel-based models: Emission factors are normalized to fuel consumption and expressed as grams of pollutant per gallon of gasoline burned instead of grams of pollutant per mile. In order to obtain an overall fleet-average emission factor, average emission factors for subgroups of vehicles are weighted by the fraction of total fuel used by each vehicle subgroup. The fleet-average emission factor is multiplied by regional fuel sales to compute pollutant emissions. - Modal emissions-based models: In order to estimate effects associated with driving dynamics the modal operation of a vehicle and related emissions need to be analyzed. Modal emissions-based models relate emissions directly to the operating mode of vehicles. The operating modes include cruise, acceleration, deceleration, and idle. - Driving cycle-based models: A driving cycles is composed of a unique profile of...