Average Vehicular Emission Factors for Air Pollution

Developing an emission inventory is a challenging exercise and the emission factors play the vital role in doing so. “Emission Factors”, by definition, represent the release of a pollutant due to combustion of fuel, with common units of gm/veh-km, under a variety of conditions, e.g., loaded and unloaded; idling; cold starts; and cruising.

Introduction to VAPIS

An emission factor is typically established based on testing a number of vehicles (with varying age and mix) under conditions listed above, to arrive at an average number. Table below presents an average set of emission factors for major vehicular categories for three fuel types (2Ws = two wheelers, 3Ws = three wheelers, LDV = light duty commercial vehicles, HDT = heavy duty trucks).

This are average emission factors based on authors assumptions; using material from variety of sources.
USE WITH DISCRETION.
(click on the image to enlarge numbers)
(for a calculator to develop a vehicular emissions inventory see VAPIS @ SIM-air)
(VAPIS = Vehicular Air Pollution Information System)

Access to local fleet specific emissions factors for inventory development is ideal.



Not all the cities in the developing world are equipped with testing facilities, which cost millions of dollars for establishment, operation, and maintenance. To view existing emission factor databases visit the VAPIS page.

A frequently asked question is the applicability of the borrowed or average emission factors. Emissions factors not only depend on the engine type, which could be common for many countries, but also local fuel quality, maintenance programs, road conditions, driving cycles, and driver’s behavior. This only increases the uncertainty of these factors established in a laboratory setting, where reality is assumed and simulated.

Where data is not available, use the average numbers comparing results from tests done vs. the vehicular technology in use, make appropriate corrections using the examples listed above (add deterioration factors, if necessary).

Where available, a considerable number of tests are being performed to establish these emission factors and where not available, cities are expected to make a close fit based on the mix of the vehicles and technology in use and and when the local factors are established, re-check the analysis.