A bottom-up modeling approach to quantify cold start emissions from urban road traffic

Cold start emissions, which are released during the first minutes of driving after the vehicle engine is started, may contribute significantly to the urban road traffic emissions. Implementation of bottom-up approaches for emission quantification in urban context is crucial to address the distribution of pollution with fine temporal and spatial resolution and to establish local mitigation measures and plans. In this research a modeling approach to quantify cold start excess emissions from road transport with fine spatial resolution is proposed and applied. In combination with transportation modeling, a new module has been developed to estimate cold start emissions at road segment level and for a trip, while preserving information on Origin-Destination of the trips contributing to those emissions. The methodology was applied to Coimbra case study allowing spatial analysis of cold start emissions in the urban context. The frequency distribution and summary statistics for road segments are provided focusing on different types of roads and seasonal variations. High contribution of cold start emissions is demonstrated with median values above 70% for carbon monoxide and hydrocarbons at local roads, where most people leave or work. The methodology applied in this work highlights the importance of cold start emission quantification for traffic pollution studies.