Untangling the Impacts of Various Factors on Emission Levels of Light Duty Gasoline Vehicles

In the last decade, climate change has become one of the major environmental issues. The reduction of greenhouse gas emission as the main contributor in climate change is now more and more critical. Therefore, precise and reliable emission estimation models are necessary to help evaluate the impacts of future projects, strategies, and policies. This increasing pressure has made the emission models more sophisticated than ever. At the same time, it is essential to understand how different variables affect emission and basically how emission models (such as MOVES) work. This study discusses and compares the contribution of each emission factor based on the available theoretical models for a light duty spark ignition gasoline engine. Since the models used in this paper are among the most precise and cited emission estimators which are based on redundant data, we focused on comparison of the factors rather than revalidation. In the first step of the analysis, the impact of each variable is calculated for a 1-kilometer trip. This is followed by an analysis for typical work-home trip. The major results of this study indicate that for a specific vehicle, the temperature has the highest contribution in vehicle’s emission. The cold start excess emission can double the total emission in very cold temperature (-40°C), all things being equal. Increasing the vehicle’s frontal area or road pavement can also become more significant than driving behavior (smooth vs. aggressive).