Second-by-Second Characterization of Cold-Start Gas-Phase and Air Toxic Emissions from a Light-Duty Vehicle

Abstract

Tailpipe pollutants from motor vehicles are linked to environmental concerns and human health issues. Gasoline engine ignition produces a significant portion of trip emissions, but few studies have quantified mobile source air toxic (MSAT) species for light-duty vehicles during cold start. Real-world tailpipe emissions were measured from a 1999 Toyota Sienna minivan with the University of Vermont total onboard tailpipe emissions measurement system. A Fourier transform infrared spectrometer measured 27 gas-phase emissions for cold start, extended idle, and warm-up driving at 1-s temporal resolution. Analysis demonstrated that (a) time to optimal function of emissions control devices was not indicated by one species, but varied for different pollutants; (b) extended idling after cold start produced elevated emissions for MSAT species as compared to warm-up driving; and (c) ambient temperatures ranging from 9.5°C to 38.4°C affected species from each emission category, with the exception of carbon dioxide. Carbon monoxide produced peak emissions three orders of magnitude higher than hot-stabilized conditions for an average of 90 s, regardless of operating conditions, while nitric oxide peak emissions were over an order of magnitude higher during warm-up driving than extended idle. Peak MSAT emissions, up to two orders of magnitude higher than hot-stabilized idle, were maintained or increased during extended idle and decreased to baseline within 100 to 200 s of warm-up driving. Results indicate extended idling after cold starts prolongs elevated concentrations of MSAT emissions, suggesting that recent policy efforts to reduce vehicle idling behavior could limit potential human exposure to the toxic exhaust constituents.

Comparison of Vehicle-Specific Fuel Use and Emissions Models Based on Externally and Internally Observable Activity Data

“…Conventional gasoline engines typically run at stoichiometric combustion conditions with a few exceptions related to cold starts and high power demand during a trip (6). A cold start typically lasts for only a few minutes (17). High power demand can occur in association with travel at high speed or at high acceleration, hill climbing, or combinations of these, but typically lasts only for a few seconds (3).…”

Modelling of the air pollutants’ cold-start emissions depending on average vehicles’ speed

“…In this paper for purposes of simulation authors use the COPERT 5.4 software. The methodology used in the COPERT model are in accordance with the guidelines from EMEP Guidebook 2019 [5,12] and widely applied in European countries. In the following Tier 3 approach, the total exhaust emissions from road transport are estimated as the sum of hot-start and cold-start emissions (during transient thermal engine operation) [5].…”

Evaluation of Light-Duty Gasoline Vehicle Rated Fuel Economy Based on In-Use Measurements

“…Thus, the engine-out emissions of products of incomplete combustion increase. Real-world measurements of an LDGV have shown cold start carbon monoxide (CO) emission rates to be three orders of magnitude higher than during hot stabilized conditions (21). EPA ratings account for cold start as part of the FTP.…”