Impacts of cold starts and hybrid electric vehicles on on-road vehicle emissions

Abstract

Incorporating cold-start emissions from hybrid electric vehicles (HEVs) into on-road emission modeling is fundamental to accurately assess the environmental impacts aligned with their projected deployment. This study introduces a cold-start emission model, integrating travel time, dynamic emission rates, and cold-start durations by fuel type. This study further explores the anticipated spatiotemporal patterns of annual cold-start emissions. Findings indicate a reliance on gasoline for most on-road vehicles in the next decade, but vehicle electrification could reduce carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOX) emissions by over 60% by 2035. Cold-start emissions will remain significant (67%-79% of CO, 59%-71% of HC, and 42%-54% of NOX emissions), especially on local roads. Cold-start emissions from HEVs will contribute to 14%, 25%, and 13% of total CO, HC, and NOX emissions in 2035, respectively. This study highlights the importance of accurate modeling in understanding the environmental benefits of vehicle electrification.