Effect of cold start and vehicle trip characteristics on spatio-temporal distribution of vehicle emissions.

Quantifying the effect of light-duty vehicle trip characteristics and cold-start extra emissions (CSEEs) on the spatio-temporal distribution of vehicle emissions at the urban scale facilitates dynamic modeling of emissions and assessment of human exposure in denser settings. The results of Beijing demonstrate that cold starts and CSEEs are predominantly distributed in peak hours, especially morning peaks. A total of 80.8% of the morning peak trips are cold-start trips, and CSEEs account for 64.2%, 50.1%, and 8.3% of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOX) in the winter morning peaks, respectively. The fraction of CSEEs for CO, HC, and NOX increases by 49.1%, 54.6%, and 36.7%, respectively, when trip length decreases from more than 35 km to less than 5 km. By converting 50% of the short automobile trips to non-motorized modes, CSEEs decrease by 12.9%, 13.4%, and 12.9% of CO, HC, and NOX of the entire road network. CSEEs are mainly distributed on local roads and minor arterials with high air pollution exposure for pedestrians and cyclists, accounting for 68.1% and 21.4%. [ABSTRACT FROM AUTHOR]