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

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 degrees C to 38.4 degrees 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.