The impact of Cold-start emissions on air pollution exposure during active travel

In emissions modeling, emissions released during cold starts are often underestimated, especially at the network level. This study quantifies the impact of cold-start emissions on human exposure during active travel (i.e., walking and bicycling) and while waiting at bus stops during the morning peak hour. Cold-start emissions of carbon monoxide (CO) are found to account for 90.2% and 77.9% of emissions on local roads and minor arterials. Neglecting cold-start emissions leads to an 82.0% underestimation of emissions at the network level. The results show that CO expo-sures are underestimated by 82.1%, 67.1%, and 88.8% for travelers walking, bicycling, and waiting at bus stops, respectively, when cold-start emissions are not considered. This study ex-amines the significant contribution of cold-start emissions and recommends taking these into account in emissions modeling. The findings concerning active travelers indicate the need for a re-assessment of potential bias when neglecting cold-start emissions.