Vehicle emissions during cold start are known to be significantly higher than after optimal vehicle operating temperatures are reached. There is limited data however, on particle number and size distributions during cold start. Cold start tailpipe emissions from a 1999 Toyota Sienna minivan were quantified at ambient temperatures between 20°C and 37°C using a novel system (Total On-board Tailpipe Emissions Measurement System (TOTEMS); assembled to quantify the full suite of exhaust emissions from light-duty vehicles. TOTEMS particle number distributions were measured from 5.6-562 nanometers using an Engine Exhaust Particle Sizer (EEPS) and total 3-3000 nanometer particle counts were measured using an Ultrafine Condensation Particle Counter (UCPC) with 1-second temporal resolution during cold start and on-road driving. Second-by-second particle number distributions from 5 cold start emissions tests showed similar particle emissions patterns, allowing for 3 different cold start Phases to be identified based on particle number emissions behavior. Cold start duration ranged from 165 to 230 seconds and increased with decreasing ambient temperature. Different particle sizes during each Phase were emitted for different lengths of time, with the most abundant particles in the nanoparticle (diameter< 50 nm) range. Themean particle number distributions showed more than 99% of total particlenumber below 100 nanometers. Concentrations of ultrafine particles (<100 nanometers) during cold start were at least 10-100 times (EEPS), and as much as 1000 times (UCPC) above hot-stabilized idle emissions. Observations also suggest the presence of tiny particles below 6 nanometers during coldstart.
Abstract